Expect it to be very busy. They are moving next fall dapper day to November instead of September, so it will be cooler, but not cold and that beats the sweltering heat of September. The heat didn't stop any this last September, it was extremely busy. I've been to 3 dapper days (two spring, one fall) and only one was kind of mellow, spring 2014 because it rained most of the time. It was annoying, but the crowds were nice.
Usually when they do discounted hotels, it's the two weeks around it, so both could be busy. Same with tickets.