Pagani doesn't race, but there has been a Zonda race car, developed by another firm - the Zonda GR GTS.
Koenigsegg is a start up who hasn't raced anything yet. If they can afford to build that car, they should be able to dig up the funds for a racing program - or at least market a stripped race car. I think they're just a little timid to really prove that the CC is all they say it is. It's easy to claim domination when nobody has seen it lose - because they don't race.
It's not really hard to build the fastest top speed car, if that's what you really want. Anyone like Saleen could equip the S7 Twin-Turbo with the right gearing and the record would be in the bag.
Either way though, the F1 carries a mistique of "the ultimate" that no other car could ever take away from it.