Most of these guys don't have safe chassis now or a clue how to built one, but you want to build bigger engines that can go 100 mph! Good luck with that and hopefully that is not what kills someone or the class.
If you want to go faster, then its time to progress to the next class. Each class has its place in the pecking order. The UTV is a great lower tier start up class. Heck even veteran racers like Marc Burnett, Victor Herrera and Larry Job have chosen to race a UTV. That's whats great about desert racing, there is a class progression. Move up to a 1600 car, 12 car or 10 car if you want to go faster. If you have real money jump into a truck class, there are several of them too.
Some progression in a class is needed to keep up with the times, but many times greed gets involved and it kills the class.