Yes! That was precisely the plan we were going with. If we were making the game without a stringent deadline the game would have 40 base spells with 3 unlocked after each battle. Ideas for the 'spell rewards' include:
- Getting back a random spell from the five you used for that battle
- Improving the damage value of a spell from your library
- Giving unique spells for having killed the monster in a certain way (using curse combo to kill the hydra might give you a stronger unique curse spell)
Not sure which option would be best.