I definitely think it makes a difference. Probably it shouldn't, but I believe that very often it does.
I'm no lawyer

but I've heard that a defendant's lawyer will usually try to persuade the defendant to dress in a manner that will make a favorable impression on the jury. For example--if a male defendant usually wears jeans and a t-shirt, long hair, and a beard, I can almost guarantee he will show up in court beardless, hair neatly trimmed, and wearing a suit and tie! Same with the goth look--it will probably be replaced by dress more suitable to a Puritan girl or boy lol!