Random thought: is it explicitly intended (for backstory etc. as well as pragmatic gameplay) that Magewars takes place in a world of Vancian magic (i.e. the system best known from D+D, where mages 'memorise' a series of spells each with a distinctive power and then, once cast, are unable to cast them again until properly rested:
http://tvtropes.org/pmwiki/pmwiki.php/Main/VancianMagic)?Obviously it wouldn't be pure Vancian magic, as you need mana as well.
If so, is the idea that an individual Mage would be able to memorise any selection of spells he wanted for a given fight, and his spellbook represents his capacity to 'contain' certain spells, or does the spellbook represent the spells he's learnt through his studies? Either of these seem to be compatible with 'foreign' spells from strange schools being harder to have in the book. I prefer the latter aesthetically because it makes mages seem more personal/distinctive: although if someone is playing 'in character' as a named Mage but wants to keep swapping spells around, the former makes more sense. Obviously some combination is possible: a Mage could formally 'memorise' (or even just 'revise' the incantantations for) a different selection of spells from his total repertoire before each fight.