I always love dressing a little bit "in costume" when I go see a show - it makes me feel like a part of the show. Obviously, it isn't enough to be distracting or impeding to the cast or other viewers - but it's like, wearing a folksy outfit with flowers to Hadestown, or a blue dress to Dear Evan Hansen, or flannel to Oklahoma, or a star on your shirt at Hamilton (which are all outfits I've worn seeing shows) - that's totally fine. For me in particular, I feel like it helps set apart the experience as a fun opportunity that would allow me to wear something I wouldn't wear in everyday life - it heightens the "theatre"-ness of the show for me.
"I think that when a movie says it was 'based on a true story,' oh, it happened - just with uglier people." - Peanut Walker, Shucked