My DD was wearing the same dress as Ariel and the interaction was still meh. I'm sure it all depends on the mood of the princesses that day but it was just dull. The food was bad and it's not something I'd repeat. We love princesses, my daughter is even named after one, but it's just not magical. I do highly recommend dressing up though. She got star treatment all over in her dress and loved it.
DDs were both dressed up. DD1 as Belle (day dress) and DD2 as Elena. Belle commented just before walking away on the fact that she had a dress like DD1, but that was the only additional interaction from any of them. As ExcitedMama said, the interaction was just Meh. But, the girls love dressing up, and they had great CM reactions everywhere else, so I agree with having the kids dress up. (The best interactions we ever got was when DS was 2 at Akershus in Epcot. All the princesses fawned over him dressed as a knight. Officially it was an Edmund Pevensie costume, but hey, they all thought he looked like Prince Philip, and who was I to argue?)