I was going to come straight out and say that the Bathurst race which evolved into a Holden/Ford duel lost it for me when they restricted the race to those two marques. I completely lost interest because the variety had gone.
At some point, which I missed, because I had lost interest, they brought the cars even closer together with the runnin gear being the same. Perhaps support has forced them to revert to more diversification.
I would like to see the organisers revert to the original concept of the bathurst style race and the cars bear more resemblance to the vehicles we buy for the road: Modifications strictly limited to safety and stability.
Having said all that, there are many one marque races around. Minis used to do it. Porsche still do it, Lamborghini I think sponsor a race. There again I don't watch those either!
Regards
Paul