I agree with almost everything you said, but I don't think that the government could change too much because there is too many dirtbike riders, sure its nothing compared to car drivers but theres still a hell of a lot of dirtbikers. Over here in Australia over 7 out of every 100 people has a motorcycle licence, yes, most are road bike riders but think of all the unlicensed dirtbikers. and I would think the numbers would be the same in USA.
I still think that its a worry that things could become more restrictive, so I think joining a motorcycle rights group is probably one of the best things you can do. Stock mufflers are good too, but I have an after-market muffler and its not really all that noisy.