Don't forget that in AP, you can trade in surplus magic crystals for runes. I plan to have high level neatness and as I am playing paladin, only learn the spells I want to use (no sense in learning any Chaos magic damage spells or Sheep, Doom, Lightning etc...) - I will keep those crystals, and trade them in for runes to boost my Rune Mages.
On Normal, you have tons of crystals, even without Neatness. I remember on my first walkthrough of AP with a warrior, I learned all the spells and got them to high levels because I wanted to test them... and I was still left with lots of surplus crystals.