Have you ever read the story of Harrison Bergeron, by Kurt Vonnegut? What we need is less rules and regulations, not more. Have a look at the motorsports that have brought in waves of new rules to keep things fair and produce close racing. Formula One? NASCAR? What do we know about these sports? Well, they were better in the olden days, and that's because the machines were different enough in capability that people could cheer for a manufacturer. Let's face it, people who cheered for Richard Petty did so as much for his car as they did for him. It was a Ford-Chevy-Mopar sport, and every couple of years, one of them would do something big and wipe out the competition, until someone else did something big and wiped out the competition. Meanwhile, the racing was intense and awesome, even though it wasn't necessarily "close." These were days when you didn't see a gigantic rectangle of cars moving in a circle at exactly the same speed for three hours. Some were better than others, and that's what made it interesting. Now, you can't deny that NASCAR is the epitome of close racing - nobody is ever more than a meter away from the car in front of them. REAL exciting stuff there...
And I don't like the idea of having this big web of different rules, where if you have such-and-such a type of engine, then you have to have such-and-such displacement, which implies that you fall into category such-and-such, which means that your bike can only have X and Y, but not Z. What it's doing is taking the motor element out of motorsport. It's turning it into a pure, 100% man-against-man contest, and I just don't think that's what people want to see. They want to see Kawasaki (or whoever) make an awesome new bike (which they can buy!) and wipe out the World Champion with a rider no one's heard of.
I agree that the manufacturers shouldn't have a word in the rule-making process, but I also don't think there should be much of a rule-making process, simply because there shouldn't be all that many rules. Someone should be able to explain the engine rules of a given class to someone else in fifteen seconds or less. "Everyone gets this much displacement to work with, in a naturally-aspirated, internal-combustion piston engine." Full stop.
This would allow for struggles between the riders, AND between machinery! And, because we would still require some production rule (not in raw numbers, but something like bikes-per-dealership or something) there would be no six-digit-priced Works bikes that would give an economic disadvantage to one team over the other. It'd be stock and tuned production bikes. The upshot of this is, every manufacturer that wants to beat their rivals in motocross racing would want to produce a superior motocross bike. If they don't, then they will lose market share by the bags full (somehow market share is measured in bags, now.) This would result in a constant, mad competitive struggle to give US, the amateur racers and weekend riders, superior technology.
The best part is, it would be fair in the real philosophical sense. There is ONE standard of measure (displacement) and from there it's up to the engineers to produce the best bike. The best bike will be, for once, the best bike, and not just the one that managed to find a loop-hole in the rules. There's no way to make the rules so utterly "fair" in result that someone doesn't get screwed over. In road racing, the rules with the twin- and four-cylinders allowed the twins to swoop in with vastly more horsepower and lay the smack down. An inferior design (less piston area, right?) was put on the regulatory welfare, but the dole was just a little too much and the inferior design BEAT the superior design. Remember the 125-250F rule? Wasn't that originally sold to everyone as a way to keep everything fair? Remember, it took the manufacturers a while to jump on it, so it probably wasn't the result of a big lobbying effort of the AMA.
I'll end this post with an analogy (or metaphor, or whatever). Two cars are lined up at a drag strip. One is a '68 Charger, built to the hilt with racing tires, wheelie-bar, and over a thousand horses on the dyno at the wheels with a big #2 painted on the sides. In the other lane, is a bone stock Toyota Prius, except for the #4 on the side. Now, should we keep things "fair" by letting the Prius go first and then let the Charger take off later, so that they cross the finish line at roughly the same time, as determined by... some guy? Or, should we keep things "fair" by having the lights go green in the same nanosecond, and let the faster car win? In the end, it's not our choice, but I say we hit the lights at the same time and let the superior machine receive the victory that it rightly deserves.