To be honest, the prerequisites are not onerous. You merely need to take 3 metamagic feats, and which three are left entirely up to you, rather than saddling you with bad ones as some sort of penalty. Any serious caster is likely to have a couple metamagics by 15th-level anyway, so grabbing a third isn't a big deal.
The real limiting factor in general is that you can only take the feat once, and it only applies to a single spell. So yes, it's powerful, but it doesn't make you a god. You can be the fireball master, but any time you want to cast something other than fireball you're on your own.
The most powerful application of Spell Perfection is, in my opinion, using it to apply Quicken to your chosen spell without paying the 4 spell levels. That allows you to cast 2 spells a round much more often than you could otherwise.
This is certainly powerful. Overpowered? I'm not sure. I think I'll have to see it in play before I can make that determination. My gut says that at the level you get it at (15th minimum), it's not. But until I see it in play I won't swear to that.