I would forget magic dart and ignite poison for sure. I would also forget apportation as it doesn't seem very useful either (although never having used it, I wouldn't be sure) with the the notable exception of getting the orb (at which point you could relearn it).
Swiftness seems pretty useless at this stage of the game, especially as you already have haste. Mephitic cloud is also a bit beyond its sell by date, so you should forget it as well.
I would ditch blink as soon as you get controlled blink, given its of very questionable usage when you are trying to escape or get distance between you and a enemy. You do need it for training purposes until then however.
That gives you 11 extra spell levels fairly easily (for a total of 13 free spell levels).
After that it gets much harder, but you do have quite a few direct damage spells (bolt of cold, bolt of flame, (delayed) fireball, mystic blast, crystal spear, OOD, firestorm). They are all pretty great, but its almost certainly worth it to ditch at least one of them for more varied spells.
Personally I would get rid of bolt of cold, since you already have pretty good non-fire damage spells (which includes firestorm since it deals irresistible damage), but its up to you. If you only get rid of bolt of cold, and all of the earlier ones that gets you a total of 19 free spell levels.
(E: I'm also not a very big fan of crystal spear (or iron shot/stone arrow). I don't find it much more useful then other spells (eg. firestorm, OOD) even against super tough single enemies it should work significantly better against, so I would *personally* probably forget it, but you may get good useage out of it, or like it, so its up to you there.)
My recommendations are:
Controlled blink is always super great, and although it is rather costly to get up there, its certainly worth it.
I'm a
huge fan of necromutation (especially comboed with sif muna), its not really needed outside of extended (where its pretty amazing), and its crazy expensive to get necromancy/transmutation that high up simply for a single spell. Since you are going into extended, then it is worth it since it gives a ton of boosts (
torment immunity, rC+, rN+++, slight armor boost, turns negative mutations into rot, +50MR and infinite sif muna channeling) at pretty low cost (no potions, turns mutations into rot, no holy weapons and dispel undead hurts you), especially since it takes a single turn to cancel it if you need potions or are scared of dispel undead. If you are planning on getting this, its probably worth forgetting another one of you attack spells so you can learn it+blink+another high spell.
Your earth is pretty high up, so you might want to consider the shatter spell. I'm not the biggest fan of it (since its useless on a significant number of enemies), but it isn't very costly for you to learn, its pretty strong against large crowds of enemies it does hurt and its decently useful for sneaking in and grabbing runes since you can use it to break through everything but permawall.
I haven't played a mage since Spellforged Servitor has come in, but it sounds like a pretty awesome spell, and you could probably cast it with just a few levels in summoning (since its conjuration/summoning). It should be worth it to at least test it out.
There are quite a few other spells that people like out there though (like Borgnjor's Revivification, high end summonings, ect) that you can try as well.
You also want to get better rF, and keep in mind that non-int stat boosts aren't that great especially on a mage.
tl;dr:
Forget: magic dart, ignite poison, apportation, mephitic cloud, blink (you need it till you learn controlled blink though), 1/2 of your damage spells (bolt of cold,
).
Learn: Controlled blink, necromutation, servitor (?), shatter (?)
Get: More rF, don't bother so much with stat boosts.