When I was talking about a partially Vancian style, I meant that spells are "pre-packaged effects" (without the ability to redefine the effects at the time of casting), not the full "memorize up to 5 level 3 spells to prepare" D&D style.
Of course, there's an often-overlooked benefit to full D&D style Vancian magic - it creates the tension of
conflicting goals by giving you long-term resources to combat short-term problems.
In a game where you can squat down and regain all your MP between every fight, you can use every resource at your disposal, because they're all short-term, but with Vancian magic where you might be expected to fight 3-5 battles, and need to cast magic for other things like flying over a chasm or knocking a locked door, you force players to make serious choices about what resources they really need to spend versus save for later, and when they sit down to memorize their spells, they have to really think of combat potential versus need for mundane utility spells. (And you can use up a spell just for divination magic explicitly to help you make that choice...)
In order for choices to be real and meaningful, they need a certain level of "dimensionality" - that is, you need to be forced to put goals in competition with one another, and choose which goals are most important to pursue, and which of multiple resources are most expendable at the moment because of what goals you are pursuing. Each conflicting goal or resource is another dimension to your choice.
When all your goals line up, when getting everything you want out of magic costs you no more balancing than getting anything at all out of magic, then you have a non-dimensional choice system.
And that's what we're at right now - no reason not to use necromancy as much as possible if you have it at all.
Comparatively, D&D's "Vancian" system created two dimensions of conflict - one was the short-term combat/long-term resource ("I might need it later") conflict, and the other was the partial information problem when memorizing your spells ("what will I need later?").
(And that was actually why a lot of the munchkins hated it - it actually punished using one strategy for every problem, and created serious choices instead of just a calculation with a single defined solution because you only had one streamlined goal - highest possible DPS.)
So no, I don't want to just rip off D&D, but at the same time, true Vancian Magic was one of the best magic systems ever devised as a means of putting real strategic choice into a magic system, and the only other magic systems that come close are things like Magic: The Gathering and possibly the Mesmers out of Guild Wars. (Both of which are also fairly "Vancian-like", as well, although those were mostly based around the explicit and arbitrary effects that each individual spell could have.)
Again, part of the problem with all these magic systems arguments is that people always just want wizards to "feel" magical in some certain way, often in a way where it means that their magic simply wouldn't have Turing-complete rules and be basically impossible to program. What we need to focus on is what it feels like
to play the game with that kind of magic.
What is important is how it changes how we play.
Goblins always sieging for no good reason makes no particular story sense, but players still do want
something sieging them, because the need for building your fortress to control the flow of a battle, and for military dwarves to have a purpose (in this pre-internal conflict portion of the game) means that players really enjoy having some direct external threats attacking them.
Magic, likewise, needs to be looked at by the measure of what it gives to players. (For starters, it means no more dumping huge "open graves" stockpiles of goblins on your fortress's front step for any necromancer to come animate at their leisure...)
If you're going to talk about a magic system, talk about
what choices you want players to make.
I do like that part, and it would be easier to give each sphere something important, if their are only a bare minimum of spells. The idea of an escalation of spell levels is maybe not that important or interesting, because the fact of *MAGIC* should be impressive enough by itself, and breaking spells apart into power levels erodes this--besides which, easy access to healing spells for priests would sharply reduce any interest or desire to go through the excrutiating process of cultivating a doctor.
And that's the sort of argument I'm talking about...
If we're going to keep the doctors from being useless, we have to somehow make magic a less attractive alternative to doctors for common problems... And that would be hard, as most players don't use doctors at all since they tend to just leave dwarves to die.
One solution would be to just plain make the priests the doctors, (and that was, traditionally, what happened in the middle ages,) and that especially makes sense if we're going for something more magic-heavy like an elven retreat, where a druid might just spit out some chewed-up herbs as a poultice on the wound to stop the bleeding and then casting some regen spell to heal a wound.
On the topic of diseases, it's also possible to just introduce common, communicable diseases that don't require an FB, and where mundane medicine or nutritional balance or else magical intervention to prevent a disease's spread become common concerns. (That is, you can have doctors for common things and priests for only serious wounds, or the other way around.)
If magic takes long rituals, then you might only be able to bless a single warrior going out into battle with regeneration before they head out (or during their heading out), but not be able to pick and choose who to heal in the middle of a fight, and leave doctors to the immediate stop-the-bloodloss problems, while healing magic speeds up the healing process after the surgery. (As they pray for a swift recovery.)
If we go with the sort of contract magic I've been talking about (and I've never really stopped pushing for) then you might only get access to healing magic (or good healing magic, anyway) until after you have a full shrine in your fortress to a god(dess) with healing magic and pumped out enough sacrifices to buy enough of her favor for a decent healing spell in the first place. (Or, for an adventurer, you have to be in a favorable enough relation with a deity that will grant that kind of spell.) That might, again, preclude choosing gods with other types of benefits to be patrons of your fortress or your adventurer.
Rather than "levels" you can also just have a basic spell that expands in power as you train it. It might be useless without constant practice, but then a potent force for a well-trained healer.
In that case, especially if we are talking about
handing over a significant chunk of fortress autonomy over to a priest class you don't have direct control over, then you might just prefer crap doctors who leave their patients to die. (At least, until plagues become common enough to warrant better medical care...) Especially if contract magic might require negotiation with the deity, or at least the priestly class who controls access to the magic (and really wants a new golden statue of the healing goddess and some better rooms for their monks...).
There might still be the occasional hurling of fireballs, etc., but I'd rather see this being something you go to the trouble of enchanting an item to do for you.
Keep in mind the problem of how any player will immediately try mass-producing any sort of magic item that is basically a "wand of fireball". Part of what makes wizards special is that they're the only ones who can use their "technology", while any random yahoo can pick up a gun.
While I'm not opposed to a casting focus that still requires a wizard who knows exactly how to use such an item (especially if it becomes a pseudo-Vancian "you only have room in your backpack for so many focuses" problem...) there's something to be cautious about just handing out the wands of magic missile like candy.
The magic user shouldn't need to switch one spell out for another (how would that even be done in DF?), and should be able to cast the same spell over and over, until he drops from sheer exhaustion (which, admittedly, for atleast most spells, should probably mean once), but I feel spells should require resources and the performing of rituals, each applied in a timely manner, rather than getting everything ready for the spell somewhere away in the background, and then speaking the last syllable at the desired moment of casting, and immediately losing all recollection of the entire spell.
This is kind of what the whole
contract magic thing was about, with players having to find ways to contract various spirits for each individual spell they wanted to cast.
Since you have to perform a service or give a payment of some kind for a pre-planned amount of magic that you can cast of a pre-defined effect (with more valuable magic being more expensive or requiring more difficult/valuable service) then you have your costs to your magic that have real weight. (Plus, you can just negotiate an open contract that allows for multiple uses, or else have a personal relationship with a spirit that lets you keep casting magic for as long as you can keep your relationship points up and the spirit happy.)
I also still think that having both a physical fatigue and a mental fatigue gauge is a good start towards preventing players from just spamming a lot of prepared spells (producing that "fall over from fatigue" point). However, you could go a bit further...
One thing from Elona is that spells require reading a limited-use spellbook to charge up spell stock that is depleted per use. Hence, some rare spells don't even have spellbooks you can buy. Casting a spell like that is like drinking a potion in a normal game, where if you use it at all, you lose it. The sense of "I might need it later" (or perhaps better yet, "I should save this spell until I have enough casting skill to actually have a decent chance of not failing") is fairly strong in that case.
For example, if you somehow became capable of innately casting some sort of magic, you might need to "charge" yourself with the respective magic type. Maybe you need to chop down nether caps and make a potion out of their magic temperature-fixing property or nether-dimensionality, and then drink a nether potion to charge up nether magic for a spell... which can have compoundingly severe side-effects as you pound away more of them.
The concept of having components also helps tie the game's resource-farming mechanics into the game's magic system, as you then reward skill at other portions of the game (like nether-cap farming) with more power in another (magic). This is actually part-and-parcel with part of the notion of the farming system's magic xenosynthesis, since it means that advanced farming techniques for magic ingredients would be necessary for gaining the components needed to cast spells.
This, in turn, could answer the question of why there would be a difference between priests and doctors, as it would mean that only a developed fortress with a temple to a healing goddess, sacrifices to keep that goddess happy,
and sufficient supplies of reagents for healing spells are going to be capable of relying on healing magic, while doctors just sort of work on their own power.