Just going to chime in with everyone else that has said that park attire is perfectly fine. We've been there for lunch and dinner and I don't recall seeing anyone there particularly dressed up. When we have gone for dinner are just at Epcot for the night, I've worn a sundress with a light sweater (it does get chilly in there!), but only because that's my typical nighttime attire at the parks if I've had time to go back for a shower and change.