The amount of contact in one BTCC race is far greater than the amount of contact I've ever seen in a club racing weekend on the same circuits and TBH series like stock hatches are hardly exactly the kind of cars where you'd expect drivers to worry about denting them, but to be fair they manage to race without driving into each other and have far more closer action as a result, I can't remember the last time I saw a big crash caused by another car that was seemingly in control or aware before he committed to a corner that there was going to be contact. The problem with BTCC is they just accept contact, I'm not sure if they actually always want to take the other guy out but they will not slow down or go off line, let alone off the track to avoid contact, in club racing and serious formulae you'll find people will do anything to avoid contact and because they trust each other to do that can then spend most of the time much closer.
The whole point of V8 supercars is that it is Ford vs Holden and TBH I don't think there'd be many companies producing simple large V8 cars wanting to enter other than Ford or GM.