I play in a grunge band and would love to say "Image doesn't matter, it's a social construct..."
But TBH:
1) When I go and see other bands, and they look terrible, like they all want to be in differnet bands, it's awful, even if the musics great. I feel the same if people play the tracks standing perfect still, like they're recording or something.
2) I feel most comfortable in my old pants, and a stained Nirvana Tee. However, knowing that I'm going to be standing, playing to loads of cute female adoring fans (ahem...) I want to make an effort.
I guess it's personal choice between looks, and performance. But I ask you, would you sleep with Susan Boyle if you knew she was amazing in bed? Nor would I.