A "touring" car is just that, a "touring" car. The BTCC, DTM & V8 supercars are not touring cars, they are race cars, based off a "touring" car.
"Touring" means driving along the road in comfort with people along for the ride. The use of the word "touring" in race classes i think is purely an indication that the cars that are racing are based off their road going counterparts.
You don't need big wings on the road car class vehicles. The little sports wings are more than enough. Hell I've got a XRT style rear spoiler on my Holden Commodore, its plenty enough. I don't need no GT style mega-airplane wing to keep me on the road at 50km/h (our local speedlimit in residential area).
Must admit though, the FXO in S1 looked sexy, but with the advent of the GTR class in S2, it was only sensible to tone down the look a tad.