We dined there as well and I wore sneakers, shorts and a "nice" plain white t-shirt. My wife wore a skirt and blouse--nothing too dressy and my two boys (8 & 6) wore jean shorts and collared shirts. We were not underdressed by any means, but there were a lot of people there dressed for nice dinner. I had heard the same thing about no t-shirts but I had no problem and I was planning on schlepping through the parts every day so I had not even packed a collared shirt.