My first instructing job, there was no requirement. I was in college at the time, and it was a 45 minute drive away, so I was in anything from slacks and a nice golf shirt to a t-shirt and shorts, depending on the time of year, and how much time I had to get from class to the airport. Next job I got was a bit more formal, but still pretty laid back. Central Flying Service in Little Rock, AR. Big 141 school, we had uniform shirts and jeans. They tried to keep it casual and laid back. Flying is FUN. People get into it because they enjoy doing it. There is nothing anywhere that says being a professional means you have to be a stiff a$$.
My first charter job, we had uniforms, but everything was specifically tailored to the customer, and they knew that. Standard was uniforms. But.....some didn't want that. One customer wanted 'casual dress'. Another wanted us to wear 'jeans and a golf shirt'. Still another wanted us TOTALLY casual, as in Aloha shirts and shorts.
The point is, look at what kind of operation you've got, who your customers are, and give them what they want. Trust me, wearing a spiffy uniform doesn't make you a good pilot. Being the best at what you do, and taking care of your job makes you a good pilot. You can wear all the uniforms you want, but if you suck, then you suck. If you're good, then you're good. Just do your job the best you can do, and let the chips fall where they may.