I think it's important to make an effort to look at least like you put some thought into being there, instead of looking like you just walked out of ... anywhere. It doesn't have to be regimented/matching - our guitarist plays in shirt and tie on stage, so I go shirt/tie/waistcoat just to go that extra bit (can't beat a bit of guitarist/bassist oneupmanship ). If he gets a waistcoat then I guess I'll have to upgrade to bow tie class, or maybe get a monocle
Seriously though, I think it's important to make an effort. I'd like to think audiences appreciate it when you make an effort for them, even if it is subconsciously.
On a purely personal note, I still joke that suits are for funerals, weddings, interviews and court appearances but I've grown to like dressing smart. I think it started when I wore the kilt for the first time - I assert that the Elephant Man would look good in a kilt. But a suit works wonders also.