Watched it in black & white last night
I though it was very fitting. There are some shots that look beautiful in black and white, especially with the lighting in the long shots of the final match. It looks reminiscent of old boxing films or something like Raging Bull. I have only seen The Wrestler two or three times, so I didn't really miss certain color characteristics (except Rourke's bleach blond hair!).
I know people say the best way to watch a film is how the director envisions it to look, but I say The Wrestler is worth watching in black and white. You should give it a shot, for fun's sake.