Ya but the SL is not a track car, its a luxury sports car, whereas the S2000 is a track car.
All im saying is they're comparing apples to oranges. Why not track a vette with a x5 or a c300 with a sports bike? Its not about the $.
What is and is not a track car is your opinion. The purpose of running sports cars on a track is to see how they handle extreme conditions & how truly "sporting" they actually are by evaluating them in terms of objective times & subjective behaviors against other sports cars (such as cornering transition behavior, brake fade, acceleration out of corners, etc).
Aside from the above, you said it yourself. The SL is a sports car (2 seats, low ride, VR rated tires on low profile rims, a high HP V8, etc). In fact, SL = Super Light (SLK = Super Light Kompact). Whether the SL has more built in luxury is not relavant? (911 Turbos, especially when well optioned, are quite luxurious...as is a 599, am LP560, or a Veyron). Sports cars are meant to be driven in a more "sporting" manner (on or off a track) unlike the X5 (a 4 door truck variant). The bike comment is also a different class vehicle (although some sports cars can obtain faster cars than even bikes
). Some sports cars hold up well at the track, others not so well (the 370Z brakes were found to quickly fade to the point of failure that Road & Track actually stuffed one due to inadequate brake shoe metalurgy....it's better to find out weaknesses like this on a track than on a road while carrying a familly member on public roads, yes?
I've tracked my cars at Seca & I have indeed seen ~ 3 SLs being tracked (an SL500, a 550, and a 63) during the last 3 yrs. Insurance firms also classify the car as a sports car and in fact, why the SL can be optioned with an air driven suspension to flatten the car while cornering to counter natural high g loading body lean.