mostly everything these days unless your a scca junkie is mostly insured. Many teams in ALMS or even in speedvision touring have the option to insure all parts to the cars, not allowing "car junkies" to take them. And besides most peoples in R's arent going to the track everyday and have to use a splitter. And to be totally honest it wouldn't do a damn thing to a street car. But many things on the street are overkill though so.. If it's a street car..leave it a street car.. if it's a race car..well think about buying that splitter.
later
-Jon