I think a great attraction could be a "Nostalgia Theater". It could be attached to a Festhaus type of food court, and be a dining room with a huge screen. They could show POV's of old rides, (if they can be found) like the Screamin' Demon, King Cobra, Sky ride, Kenton Cove, Vortex, Firehawk.... They could possibly include footage from Coney Island in the 60's. They could buy old footage from families from the top of the Eiffel Tower with before/after side by sides....
This park has an important history. With Disney on both coasts having national draw, no one thought a large regional park could compete, and Kings Island basically started an industry! If they are going to do a "cheap" upgrade year again sometime (like with the smokehouses), I think this would be an excellent idea. (by the way, I think the smokehouse was AWESOME for a cheap upgrade! Well played indeed!)