I think the interesting question is, what do you want it to do?
If it's a methodological advisory committee, it's different than if it's a representational committee. If it's representational, then yes, you want to make it a broader group, as Mr. Baylis raised earlier. I'm not sure what you want it to be.
The other thing is, it isn't the only advisory committee. You could have a complementary methodological based committee. You already have all these other groups advising on specific surveys. There is not a right answer.