I've played a lot at the same venue for close to 30 years. There was a dress code. Gentlemen had to wear jacket and tie. If you didn't have one there were loaners. Now you can wear cutoff jeans and a tee shirt if you want...as long as you have a couple hundred to spend.
Most people still dress nicely, but not like before. The entertainers and wait staff always wore tuxedos. That has relaxed too. I've seen entertainers come in looking really scruffy, then wonder why they don't get asked back.
I make it a point to dress maybe a little nicer than most of the customers, so I always wear a sport coat at least.
I must say that children seem to be always well-behaved, although many of them bring their babysitters, a phone or tablet of some kind.
I don't expect people in this atmosphere to sit and watch everything I do. The ones that want to do that usually sit pretty close to me when possible. Others want to converse at their tables, which is fine. Very seldom does anyone get so loud that it is disrupting. On the rare occasions that does happen, the staff and owner are really good at handling it without causing problems. They will go over and start a conversation, ask how they are doing, maybe bring them something free to eat or drink and diffuse the situation. VERY rarely it will reach a point when they are asked to settle down or leave. Point is they are not allowed to disrupt the enjoyment of others.
I'm sure this is not the norm these days though. I've never had a problem at nursing homes or retirement centers such as described by Mark, but I haven't worked them in several years. Now most of them are owned by some huge corporations somewhere and maybe the atmosphere has changed.