My team despises wearing unis to school! We only wear them for pep rally days, which occurs twice a year or special occasions. Our falculty isn't against it, because it is school issued. Instead we do spirit days for football, because the season is 10 weeks long and one game is before school. We do a team shirt day, class spirit day, and other fun days. We have games twice a week during basketball so we my have random spirit days, but we usually don't. However our team had a great season this year and it was our schools 60th anniversary so we wore gold chains and spirit attire a lot lol.
Personally, not wearing a uni is more sanitary. Even if you don't sweat having to wear the same thing for over 12 hours is uncomfortable in my opinion if you were liners especially.