Hey, here is my suggestion
There must be difference between demo racer and racer who has a license. For example in demo server if demo racer cant take f1 car, the racer who has a license should use f1 and the other cars in demo server, so there will be difference between demo racers and license racers. And I exactly think that it will effect the demo racers and they will buy license to win races in demo servers!
If its possible u should do something on demo servers for users who has license. THEY SHOULD USE OTHER CARS ON DEMO SERVERS!