No, actually a lot of guys race R/C cars because they LIKE to work on stuff to see if they can make it better. Not everyone just wants to come out and drive. Racing by nature is driven by a competitive spirit and I'm not sure that I've ever met a racer that would turn down some extra horsepower if offered to them. I would venture to bet that there are some oval guys out there as we speak trying to figure out a way to tweak a 17.5 brushless motor to give them that little edge.
It's that competitive spirit that keeps the products and sport as a whole evolving. If everyone were complacent with the speeds that are available, nothing new would be invented and the current crop of racers would eventually get bored an move to a new hobby.