The SCCA Touring Car class required a stock unibody and outer panels (no roof mods or "template" cars, though a cage was required), factory suspension pick-up points and geometry, and factory block and head. Body mods were limited to front air dams and side skirts, though the car could be lowered. Tire sizes were commonly-seen street sizes, though obviously of a racing compound. It used popular, common mid-size models like Dodge Stratus, VW Jetta, Ford Contour... you know, cars you might actually have in your driveway. As a bonus, they turned in two directions, didn't have banks to artificially boost speed and driver "talent", and were surprisingly fast. It was great, door-handle-to-door-handle racing in recognizable cars that actually exist.
So, of course, it failed to attract an audience... because North Americans want to see 1960s technology on skinny tires in identical chassis, powered by engines with no basis in production reality, driven by southern-drawl rednecks and wrapped in skins that we can name only because someone painted the name prominently across the schnoz. [smilie=e:
The European touring-car series, I'm told, is wildly popular.