Not to mention VESA cant stand anything that could lap quicker or get faster top speeds than their beloved V8SC's. It would be good but you need to guarentee X cars at each round and put up with as MrBoost says being in a mud pit somewhere...
The top speed would be a no brainer even though the Super Taxis more then likely carry better corner exit speed because they have more resources to set up the suspension and have professionally tested aero packages.
As for the big events I think it is really a dollar issue to get on the V8 Supercar support bill, the field sizes would have an influence but VESA would turn a blind eye to that if you rock up with a truckload of money (look at the Mini series!)
Sports Sedans ran at the Adelaide GP and at Indy in years gone by, even the race of of a thousand years back at the end of 2000, does anyone know how this came about or was the class just asked to show up?I think the commercial element has come into it now days and to get on these big events you need to bring in the cash.