metamagic..
I played a druid in a game where we used the metamagic variant from Arcana Unearthed.
Your feat is useable 3/day, does not need to be prepared ahead of time, and does not raise the level of the spell. But it DOES raise the 'virtual level' of the spell to the appropriate spell leve, and if you can't normally cast a spell of that level, then you cant apply the metamagic to it.
IE, a 7th level wizard could use his Empower spell feat on a Scorching ray, spending his 2nd level spell slot and 1 use of the feat. Because he can cast 4th level spells. But he could not empower his fireball spell or his Ice storm spell, because he can't cast 5th or 6th level spells yet.
I only ever took extend spell, and Empower spell, but they were very useful.
My most common tactic was to cast Exended Mass lesser vigor on the party, to do a TON of healing over time. Empower works really well on the spike stones spell. Huge area, and lots of little d8s if they want to get out of the area.
Breaking normal spell casting level limits seems to mess up a lot of peoples games...See metamagic rods and why so many people hate them.