We have a standing instruction for students that any more than 30 and it's time to go around and try again. Having said that, it's not the bank angle that is the issue, it's the corresponding pulling back the stick and increasing the angle of attack while then crossing the controls with opposite rudder that is the issue.
Facthunter, I can tell you right now that a 172 has a bite in particular manoeuvres that very few people know about, so even the benign ones will bite hard.
While mandatory spin training would be fantastic, I suspect economics comes into it a bit. A lot of the RA aircraft aren't even guaranteed to be able to recover from a spin and aren't certified for it, although I suspect most probably would be recoverable. Frankly I think every pilot should be aeros endorsed, then you actually understand how an aircraft behaves on the limit, but once again economics wins there. But that is the reason the military teaches aerobatics to its pilots, not because they want them to have a lot of fun, but they need people who understand what the aircraft behaves like in all areas of the flight envelope.