for me battery life doesnt really mattery since i mainy play handhelds with an ac adaptor. if 3d gives you headaches turn it off its that simple. ive also heard the street fighter 4 runs a better framerate if you turn 3d off.
You need to go into the game options as simply keeping the slider down isn't enough, but you're right. And it's probably how I'd prefer to play the game in the long run, it's not a type of game that really benefits from the 3D.
I think the upcoming 3DS Mario will be THE game to determine if 3D has a legitimate use for games or is just a cheap gimmick. There were times in both Mario Galaxy games where I felt having some depth perception could've helped a lot, and if it doesn't actually make a difference here then 3D really doesn't have much of a purpose afterall. I'm expecting it WILL help though, even if it ends up being that only a few genres (namely 3D platformers) see actual benefit.