I picture something like:
Very nice.
Personally I'd pull back the magic attributes and use Inspiration/Creativity instead of Potency (i.e. that "smarter mages are better mages" and also makes sense, a character who is cleaver will find more efficient ways of spending his available magic, which also matches up with preconceived notions and ideas as well as existing literature).
One thing I've noticed here is that a lot of people seem to be assuming we need to have just one single way to use magic. Why would we want that?
We can have memorization systems, tiredness systems, ritual systems, and so on all as different options. Different races might have radically different ways of using magic. (Of course, there should be some
underlying metaphysical commonality so they can interact, dispel each other, etc, but the way they draw on that basic raw magic force could be radically different.)
And, to get back on topic, this could be reflected in stats, too. "Magical" creatures like demons and faeries could have a stat that represents raw, innate magical ability; perhaps even elves could have a bit of this. With a high enough value, you could use magic based on this without much intelligence at all; it would be used for more 'innate' sorts of powers (which just tire you, or consume some sort of magical force.)
MP I agree is too abstract for the Dwarf Fortress universe, but something vaguely similar could still be used, especially for magical creatures -- some measure of the amount of magic they have stored in their body. Different creatures could recover it in different ways or at different rates (vampires, if they exist, would drink blood; elves, if they have it, would recover it faster near trees, and particularly near their named special trees in their elven glades.) If you're playing as such a race, you wouldn't get an exact number for your magic reserves; you'd just have a general sense of them. Or it might be expressed as 'tiring' you, since that magic is a part of your general energy. But from a metaphysical standpoint, you're feeling tired because you've started to exhaust the magic that is an essential part of your being, and you need to replenish it soon.
In fact, I think it would make sense if all magic requires some sort of magical 'power source', but that the way you get that power could vary wildly; not everyone would have it innately...
But this magical energy could also be stored in objects -- a human might not have innate power to draw on, but they could get (or steal) a piece of wood from those sacred magic-filled elven trees, or a magic rock with a certain amount of power in it, or some special herbs you gathered or grew that contain a bit of magic you can use. Some artifacts would also contain magic (and you'd want materials containing magic to make such artifacts, too -- which could create a
lot of conflict with the elves, who of course have those valuable magic-producing trees that everyone wants to cut down so they can use their wood.) Humans might want to create wands out of the wood of elven trees, say.
Objects containing magic might or might not replenish that power over time, or only recover it under certain circumstances. Artifacts should probably almost always have a way to replenish it, though that could vary from artifact to artifact (an artifact weapon or armor might require that it be splattered with blood to recover it -- in fact, any artifact might require this. Others might draw on sunlight, or from water, or by slowly weakening those around them. Some might just recover it innately (they're drawing it from who knows where.)
Things like magic-containing herbs and rocks would probably be mostly expendable (though herbs would probably be 'used up' anyway. Magical-storage rocks could be charged if you have another source of magic to draw into them from, perhaps, assuming you have the skills and talent to do so.)
Deities and other powerful entities could provide non-magical entities with an innate magic pool to draw on, too. (The proverbial 'deal with the devil'.) This might or might not be the same as being a magical creature yourself.
For races without innate magic, intelligence, inspiration, or whatever would be more important. There might be a stat that represents a kind of 'folksy' innate understanding of magic (or perhaps this would be a skill.) Some races, like Elves, might combine some limited natural magic with intelligent study; others might depend entirely on one or the other (humans and dwarves would probably depend on using magic drawn from objects or other sources; demons and unicorns would get their magic entirely innately.)
Of course, magic could also have a 'flavor'; if you kill a demon, its claw might contain magic you could use, but don't expect it to be useful for magical healing! A unicorn's horn would be much better. Likewise, those magical herbs you collect might not be useful for anything
but. Things like artifacts might have a specific way they're supposed to use their magic (which might not even require any skills or anything); but someone skilled in magic could perhaps still draw this power out for their own usage.
Some rituals might work for people with no innate magic, without having to have a magic-filled object to draw on. These rituals could be powered by a deity or some other entity under some ancient contract or understanding to respond to them; or they could be a secret way of converting something else into magical energy (animal/human/dwarven sacrifice, for instance.) Or perhaps those sacrifices are just a way to get some entity to provide you with the power you need.
Rituals would be a way to do 'prepared' (or 'memorization-style') magic, for those who practice it. You're making a deal in advance with some entity to do what you want at a later time... or you're charging yourself or some object up with a particular effect to be discharged later, or whatever. Of course, preparing some of these abilities wouldn't be as simple as just sitting down with your book to memorize -- some could require animal sacrifice every time to make a deal with whatever entity you're using to prepare for it. Others, though, might be simple to prepare.
Just some thoughts, anyway.