I've been to the one in Dallas, while up there at a Sci-Fi con a few years back.
There were folks there in everything from t-shirts to Renfaire garb, so my kilt and polo shirt went pretty much with out notice. I didn't have an issue, but as some have mentioned it can be messy, so I probably wouldn't wear my nice wool kilt there. It was not cheap, but a good show and fun time.