I don't know if changing the date would change attendance much at all. You might get a couple of people that normally have family obligations on Labor Day, but you might lose a couple of people that can't swing it without a long weekend. As for us personally, I can't comment on a 'best weekend' for next year as I have no idea even about what time zone we will be in this time next year.
I say plan it for whatever works best for you guys and those that can, will; and those that can't, won't.
Rachel told me last night that we WILL be there for at least some of the weekend this year. I have my Friday shift covered, but am still waiting on Saturday afternoon/evening shifts. Worst case scenario: We fly up Friday, spend the night Friday night, stick around for as long as possible on Saturday and then one of two things will happen 1.) Rachel and I both come back to Ames and call it 'done', or 2.) I come back and work and Rachel stays up there Sat night and I fly back up Sunday to get her.
THAT'S how much my non-pilot wife has fallen in love with the 6Y9 fly-in: She won't go to OSH, but she is willing to spend the night alone at 6Y9 just so she can be there all weekend!