I will agree that a not so great day is better than no day. That said, my xsil and her now XH took us for our first visit back in '97 I think. The girls got really cranky because it was hot and their parents fought and bickered the whole time. They got so mad at each other that one took one girl and was headed back to the hotel so she could nap and the other followed arguing the whole way. He said they got in a big argument up by the gates and two off duty cops interneved and told them they were ruining it for everyone around them. They could either cool it or they'd have them escorted out.
It just put tension on the whole rest of the trip.