I have the base game plus Tomes 1 & 2... so plenty of spells to go around... but even then, you still need to determine how to "share" all of those cards when drafting between 2 players. Here's what I've come up with that works well.
1) Player's spell books start with the recommended starting books for all 4 mages to begin with.
2) Divide up all the remaining spells into their school of magic and card type (creature/conjuration/etc.)
3) Players automatically get all remaining spells in their school of magic.
4) Players take turns picking up one of the piles of cards on the table until they've all been chosen.
For example, I'm playing the Wizard, so I start with all the spells in his recommended starting spell book (to provide a good "base variety" for each mage). Then I also get all the remaining Arcane spells in all the various card types (all arcane creatures, incantations, etc...). My opponent (Beastmaster) does the same with his mage. Then on my first turn, I decide to take all the remaining dark attack spells. Then my opponent takes all the remaining holy incantations. Then on my turn I choose all the remaining holy creatures. etc. etc. etc... until all the various piles are selected.
Then we have a fair distribution of all the cards to tweak/build our spell books, and it keeps both players in the dark as to which cards they're putting in their books... because you're no longer drawing from a common card pool and can't "count cards" to see what's been taken yet or not.
Another nice thing is that it really doesn't take much time at all to divide up the cards either. Once two complete schools of magic are removed from the remaining cards, it goes real quick.