[Kameron8]

I would like to propose an alternative:

Make copy spells only good for one cast. After that, it's gone.

Realistically this is just going to encourage people to preload spells over and over before each fight. Grab Fortune Wind, Sanctuary, Quickness, Red Sea, whatever you want, then run on back prepared for a fight. I'm partial to making them default to level 1, since most of the spells that are crazy to steal scale with level more than anything. (Some notable examples being Death Knighting, Quickness, Sanctuary, Overload, and Needle.)