I used to work in a busy bar wher every weekend there were various groups in fancy dress. They certainly weren't targeted by thugs, if it's in a city most people would be used to seeing people dressed up. Anf yeah, I'd say the groups in fancy dress did get more people going over to talk to them and comment on their outfits.
I used to hate the groups though cos every single one of them thought it must be the first time the staff had seen such a hilarious site as people dressed in fancy dress! (Mind you, I was a notoriously miserable barmaid so I wouldn't worry about that!)