1. Different strokes for different folks. Some churches are more formal. That's perfectly understandable.
2. The more contemporary church that "doesnt care what you wear" has already developed its own uniform comprised of skinny jeans and such. If you walk up in a mega church with a shirt and tie on, the stares will be just as many as blue jean tshirt guy at First Prez downtown..and I go to a contemporary church.
3. The whole "I wear my best because I am blessed" argument frankly stinks of prosperity gospel. I mean I get the whole respect, it's the way I was raised, it's the appropriate/expected clothing arguement and I can support that, but the second you start saying I wear this to show I am blessed, well dang Pharisee, just get you a purple robe on.
4. We have to admit the whole "put on your Sunday best" is perhaps the best illustration of the failings of the modern Christian. Live life however Monday through Saturday. Put suit on and find a local church on Sunday. All good.
At least the relaxed dress crowd tends to recognize that faith isn't about Sunday mornings.
5. There are plenty of folks who wear their Sunday best who are not pretentious, as there are many blue jean guys who have a heart and respect for Jesus that frankly a nice suit wouldn't improve.
6. Let's be honest, very few churches whether they are rigid and formal or progressive and contemporary REALLY know how to interact with real poor folk. Nor are they prepared to do what it takes to get fully involved in the lives of people vastly different than them.
That kind of Jesusesque ministry is messy and scary whether you wear Brooks Brother's or Affliction.