It has always seemed normal to me to come to church wearing good clothes... I mean, when you're visiting friends, you dress well, so why wouldn't you dress well when coming to God's house?
I don't care what you wear in your everyday life, be it suits, denim, or torn up T-shirts, as long as you dress respectably in church. The only case in which I'd tolerate it is in countryside churches in Russia, Serbia, Romania or other Eastern European countries, as people there may be quite poor and don't always have enough money to buy clothes that they don't need to go to do their jobs, which are quite often in workshops, factories or fields and thus don't look too good.