I dressed in a full Snow White costume last year and loved every single minute of it. It was truly a dream come true, to go to Magic Kingdom as an adult dressed as a princess. I think if Disney opened an adult BBB, they would rake it in!
We did this the first year as the Sanderson Sisters (Hocus Pocus). I am so glad we did, it was mid-September and even at 10pm still hot and humid.
I definitely recommend some type of themed clothing, whether it is a full costume or just a pumpkin shirt. Whatever fits you best!