I agree on some spending limit, $3000 is reasonable. What I don't agree on is that rule that people can buy your bike out from under you inwillingly. I'm smart and resourceful if I do say so myself, and a rule like that would mean just building everybody else bikes in a negative way, because I know how to make good use of my money.
I like the way club auto racing does it:
Practice
Qualify
Race based on qualifying results
Everybody gets all the track time they paid for, and nobody sits out a heat. Slower guys filter to the back and enjoy racing amongst themselves (the whole point, is it not?).
If there is a major dispute over the legality of a machine, you tear it down at the track, look inside, and come clean. Common sense per situation will determine the outcome. I don't think shame is beyond anyone if there are 20 other racers looking at them in disbelief.
You'll never be forced to sell your time and craftsmanship to somebody because they're upset that you're fast, that's totally lame in a club racing setting where people care about their bikes. They're not crapbox Saturday night spec dirt racers or Chumpcars, people put heart into these things and use them to get around and recreate.
Other than that, I like the idea of doing an enduro, especially with mixed surfaces where knobbies or ATB tires might be appropriate. It would be cool to see an emergency happy time engine change pit stop!
If somebody's really fast, just stick them in unlimited class like last race with the Tomahawk mopeds. The point is not only to go out there and compete, but also to get enough track time to sort your machine and practice and enjoy riding. I wouldn't care if somebody stuck me in unlimited, I'd just race with whoever else got put in unlimited class and try to use my brain and balls to make the bike go faster, a fun challenge instead of going out and cleaning up. I say if you have a need for a faster class for somebody or a few who dominate, make the class as it doesn't affect the grid order, just gaps between split starts.
I for one, just want to go out there and go as fast as I can, if there are others in the same speed bracket, we can have fun racing. If you really want to get technical with rules it would benefit the sport to have an official sanctioning body with sport-wide standards, kinda like the FIA does for international motorsports conduct. Having a sanctioning body of sorts would legitimize the sport and make it eligible for the mainstreaming that other sports have benefited from in terms of financial support. Then racers could build bikes that meet class standard definitions and rules like in NASA and, ahem, SCCA. You know what you can expect and what you need to do, so you can focus on what is important, having fun and racing fairly.
The big rulebooks sure are a pain to go over and scrutinize, but it can be fun and inventive to manipulate loopholes, and at least you know what your limits are in writing, which is "legally" binding within club racing events.
The auto racers I work with complain on time or another about slower traffic or getting dive bombed by faster traffic since there are mixed formula classes on track. The drivers that have problems clearing corners with such differentials in speed usually have problems with situational awareness. It's hard to pass or be passed safely by someone on par with your speed. Mirrors on both sides of a race bike will help your situational awareness, and in big speed differences it will be a simple point by if needed.