See, that's one reason that I like being the bass player... I DON'T HAVE TO LOOK GOOD!!!
I hang out on stage, move around a little to take up visual space on the stage, and that's pretty much it. I show up to the gig in whatever I wore to my full time job that day, I might shave, or not. I'm not terribly concerned about my appearance. But the vocalist, being out in front, I think should be more presentable than the rest of the band. Not necessarily better looking, just more put together. The frontperson of the band should be the "eye-candy" for the crowd because that is who the attention is focused on.
Philby mentioned David from Disturbed -- great example! He's got the piecings hanging from his lips, shaved head, and a quiet demeaner (from what I've seen of the guy anyway). Kind of a intimidating looking guy. But when they put on a show, he's always full of energy, dressed better than the rest of the band, well spoken when talking to/with the crowd, etc. Everything is still in the context of their music, but he is clearly the frontman.