I have no idea how much any of these things would cost so therefore do not know how possible they are, however my first three would be :
1) The floor. I don't know much about the technical side of it, but it looks very tired. Possibly not a new floor, but the key especially needs some new art. You spend more time looking at the court than anywhere else so make it look good. Make it look like a professional team plays on it.
2) New scoreboard & PA system, for obvious reasons. I imagine that would be very expensive.
3) Put up the rest of the team photos. Fix up that god awful part of the wall where Davis' jersey hangs and put up something that is worthy of a legend. In fact, find someway of honoring past players who are not going to have their numbers retired. Make a feature out of it.