I'm still defending what I said, in that in that at least in the genres I'm interested in, clothing is not that important. Look at what the Arctic Monkeys, Blur, Sonic Youth, Pearl Jam, and countless others wear on stage. Jeans and a t-shirt and a pair of comfy trainers usually! All of aforementioned bands have played on the biggest stages. If they listened to half of the fashion advice being thrown around in this thread they would look ridiculous!
Sure, having a look can make you stand out but your musical talent should be enough to get you anywhere if it's good enough. Look at Tommy Riley, recent winner of the T4 unsigned competition. He just looks like any other kid his age, wearing the same kind of clothes as the man on the street.
I accept that certain bands have that theatrical performance element where the image is a big part of it, and that function bands / posh jazz outfits have to dress smartly to fit in. But that's just not most bands. Saying that Marylin Manson wouldn't have got where he is without his look is perhaps a valid point; but that doesn't mean that anyone else can make themselves successful by simply dressing like a freak.
Most of these bands just wear whatever they want and still manage to look cool. Of course, if you're the type of person who wears a football shirt whilst playing a gig then you've obviously got no fashion sense whatsoever, and sprucing yourself up a bit is the right thing to do! If you're cool, you'll look cool no matter what you wear. If you're not, you'll have trouble looking cool no matter what you put on and will often look like you're trying too hard!