If the AMA wants to discourage this stuff, forget fining them. $500 isn't jack to Bogle and Stewart. They probably have that crinkled up in their summer shorts and they're unaware its even there until the next time they wear them.
Anyway, all AMA needs to do is put a penalty box by the mechanic area, give them a Purple flag and send them to the penalty box for 1 lap (There last fastest lap time with an official holding them back with the stop watch.) That's a fine that everyone wouldn't want, and nobody would be Punching each other on the track.
Now I'd be for this fine for physical altercations....punching, fighting etc. Not for rough/borderline/takeout style passes. But whoever gets punched they both get the penalty box. The guy getting punched and the guy throwing the punch.