How about some delayed gratification in Pathfinder?
Storing Energy-Metamagic Feat-When you prepare spells, you may select any number of spell slots and prepare spells in those slots. If you do not use that spell that day, the next time you use the spell any effects of that spell are multiplied by 1.5. If you do not use that same spell slot the next day, the multiplier becomes 2. The multiplier for spell effects never becomes grater then 2. Any spell that is stored does not change the level of the spell.
I like this one, BUT should the character lose hit points equal to the spell level they are storing? So if you store a fireball, you lose 3 hit points and they cant be healed till you use the spell? Thoughts gang?