The flight school I worked at was 141 but small, and all the instructors wore uniforms, ties, epaulets. This included the chief pilot/owner, who was never out of uniform unless he was working on a plane. I was not a huge fan of it at the time, but I talked to numerous students who had chosen the school over others on the field because we came off as more professional. I know it was mostly a marketing ploy, but it also saved the owner the hassle of making decisions obout whether or not an instructor was appropriately dressed.
Sure, I felt a little goofy getting out of a 1970's 172 in a uniform, but it saved the trouble of deciding what to wear in the morning. And there were other instructors on the field who'd wear flip flops and t-shirts, which to me looked a lot stupider.