We get a lot of tourist traffic in my church; people come off the street "as they are", and that's just fine. The regular members all dress for the occasion, to one degree or another. It's not something anyone had to be harangued into doing, we just do it.
At one time a harangue wouldn't have been necessary; people used to just have a sense about these things. My own guideline has always been that if I wouldn't wear it to work, I wouldn't wear it to church-- but when I take a look at some of the "workplace" attire these days, wow. Too many girls don't see the difference between dressing for work and dressing for a hot date.