I would like to see the development of a new dining/shopping area that would connect the main park with Boomerang Bay. The area would be behind the "middle ground" between the two parks. It would be connected by paths and could possibly be reached by riding the train (don't have its route memorized real well). I think that with this placement, it would be sort of a "destination" that would lead people through both sides of the park, and would facilitate more movement between the two. Possible place for hotel down the road, as well (people brought in by monorail?).
I am really impressed with the water park, and I think this development would tie it in more with the main park. I think the time is coming for an all-new area. As much as I would like to visit Kings Island circa 1975, its all-new, brand new experiences that keep bringing people in.