Well, I have to disagree that Valleyfair has no meaningful competition. Adventureland just got bought by Herschend Family Entertainment so you know they are going to put a lot of money into that park to bring it up to their standards. And, this year a brand new park in Waterloo, IA, Lost Island, will open. How is this not competition? I don't disagree with your waterpark assessment, but a 350K sq ft indoor waterpark is a different product then any outdoor waterpark. In the summer, most people go to a waterpark to get SUN. Can't do that indoors.
Cedar Fair has to know that they really need to tackle both the dry park and the waterpark, and they don't have a decade to do it.
BTW, Excalibur has it's train in the station and is ready to go for this season. I'm hoping that they are re-evaluating the need to remove Excalibur and are working on a plan to expand the waterpark and keep Excalibur.