Took ~70 days but I'm glad the spell system is getting a rework. While I understand the concept of a card/combination system, I believe the priority should be on allowing the end-user (player) to have fun with it in a meaningful and understandable way. One must balance depth and complexity in game dev.
High Depth & High Complexity = Path of Exile skill tree
Medium Depth & Medium Complexity = WoW TBC skill tree 'talent' system
Medium Depth & Low Complexity = Zelda LttP Item System
Warning: Unsolicited advice ahead
There are many ways to do it, but perhaps consider a UI-based system that allows players to see all their available spells and then create their own custom 'decks' so they have some semblence of control over what they are using. This also mitigates the whole 'I got a new card but where did it go and why can't I use it' feeling.
It is wonderful to see this game take shape :)