Have you ever tried to get a friend to start watching the NBA? Usually the first comment out of their mouths is "I don't understand what a foul is." That's because from one game to the next - and even within the same game, what qualifies as a foul seems pretty subjective at times. The refs just aren't as good as they could be imo.
The glaring problem with NBA refs is that they are allowed to police their own. They are supposed to review and reprimand any underperforming refs with the ultimate authority being the director of officials - himself a referee.
This. Never. Works. Any psychology undergrad will tell you that people cannot be trusted to police themselves because they always have their own best interests at heart. Nobody wants to fire one of their own for incompetence. It's the reason that any investigation in police misconduct for example is invetigated by the department of internal affairs - a separate and presumably more neutral third party organization.
I think the NBA could do two things to improve the quality of its refs:
1) Create a neutral third party to review referee performance and hire/fire refs.
2) Change the rules such that each coach could challenge a call once per half. I don't think this would have an adverse effect in terms of slowing down the game. You could even remove one full and/or one 20sec timeout from the current allotment to compensate as I think they're too many timeouts in games anyway.
How many times have we seen a blown call on a big screen instant replay with no repercussion for the ref? Too many times for my liking. With a challenge system like in football, the ref could get immediate feedback on his error and it would be very public as to just how good a particular ref is over time. The penalty for an erroneous challenge could be something like 2fts and loss of possession. I don't think one challenge per half would be detrimental to the speed of the game.