My experience has been no correlation to the number of races, have had crash free 50 race seasons. Crashed more in Cat 3 than in 4 (there was no 5), 2 or Masters. Saw fewer crashes on the Track than on the Road. Road Race crashes were more severe than Crit crashes.

Would like to add that i've known a couple of riders who were ****-magnets. They wern't the worst bike handlers, didn't take unnecessary risks, but if there was a pileup they were in it or behind it. Perhaps they had some Karma issues? Unexplainable but it just seemed like they were always in the wrong place at the wrong time.

edit: I think the 80-20 rule would apply well here. 80% of crashes caused by 20% of riders.