I agree with this, definitely. I feel like a hard limit, or something like a mana pool would not be in keeping with the spirit of the game. Super Smash Brothers: Brawl has a system to discourage spamming attacks similar to one detailed above. Basically the last 10 attacks you make are stored, and if you keep using the same one it gets weaker and weaker. You can reset your moves by doing ten other attacks and then re-use the one you want to use at full strength. This might add an element of strategy to the game, and should solve the spamming issue. I think this should be in PvP as well as PvE, since it is a lot more fun when you use a variety of spells (though this is a personal choice).