When you talk about cages, there is nobody RACING without one. Period. There is a clear line drawn right there, with no compromises as far as i have seen anyway. So within the realms of this question (about cages) it's a relevant point, and distinction made everywhere for good reason.
Brings me to my second point addressing your question Stuart, if i want to piss about in a NON-RACE category primarily intended for road cars well i have to accept that CAMS rules aren't the be all and end all in that arena. They are guidelines with a thick overlay of compromise to deal with the fact that people drive these cars on the road every day. Well, some do.
Anyway I believe anyone who wants to participate in a real CAMS Sports Sedan championship, with unadulterated CAMS rules, should... a) actually get a real sports sedan and b) go racing against real sports sedans in a c) real sports sedan championship. Simple.