You definitely shouldn't look too nice in a metal band mateNeither Slayer nor Anthrax used to wear uniforms but I guess people and priorities change. There is also nothing wrong with looking nice. In all the metal bands I have played I always looked nice, maybe too nice and got shit for it from some people until they saw me onstage playing. Then there was the classic: " holy shit I didn't realize you were the drummer, I'm sorry dude!" Followed by a free beer.
Like I said, there's always the image thing to consider to a certain extent but the only guy I've seen get away with it was Serj Tankian who came out in a very nice, white, long-sleeved shirt and proceeded to crush it with System Of A Down.