I would pick September 22nd. It's before the season really gets heavy and therefore easier to get rooms/tables. It's also the same weekend we went last year.
I just called the ol' Motel 6, and yes they would love to have there again, and the manager is going to call me on Wednesday with the range of group rates. It's usually $129, but last year they offered us $99 and then dropped it to $89 by the time we arrived because we had so many.
Right now, just about all weekends are open, but I really prefer the September dates - for the weather, the crowd, and the tiny fact that the town is, um, how you might say... fresher?
OK, to the punch, who doesn't like 9/22?