I absolutely agree with everyone who suggested getting a neuropsyche reevaluation. We had one last year for our 6-year-old - the first one since her original diagnosis at 26 months - and got tons of great information about where her strengths and challenges lie. Definitely helpful, and we were able to take the information to the school and update her IEP accordingly.

My son was diagnosed in March with Asperger's. In May the criteria changed for all ASD diagnosis. I didn't worry about it until Medicaid refused to pay for his ABA due to him not having one of the diagnosis they cover. It's stupid and their information they are basing coverage on is 12 years old. But I talked to his psychologist and she updated his dx to ASD code 299.0, so that he can get on the list to get covered.

It all depends on what it can help with or hinder. Weigh allthe effects carefully. It doesn't change who your son is at all, but it could render him serviceless if he were to longer meet the diagnostic criteria and be shut out of possible needed help in the future.

I guess what you would need to ask yourself is what you would want to achieve by getting him re-evaluated. Do you want him to "lose" his diagnosis? Do you feel that would be better for self image and self esteem? Would it be disruptive to his services to lose his diagnosis? If he were diagnosed under the new standards and he was now considered off the spectrum (if for instance he was diagnosed with social communication disorder) what would that mean for him, for your family, for his education?
It's a very personal decision because it depends a lot in what you're trying to achieve.
One of my twins would probably be considered "recovered" from his diagnosis, or more accurately diagnosed with something less than his current classic autism diagnosis but I've decided to just leave things the way they are. I don't want to upset the apple cart, so to speak. I'm afraid of what that would mean when considering services. But what's right for our family might not be what's right for yours.

School age children should have a reevaluation every 3 years.

A reevaluation will tell you what areas he has had success and what areas need more attention. This may help the teachers and staff working with him to get a better picture of how to service him.