I say an aquarium...shopping...dining...maybe lodging, would all work well here. Plus, paint and grease some of the rides, retheme, and open up the gates!
With the reno at Wonders of Wildlife up in Springfield, I doubt you get your wish on the aqaurium. I can't figure out what retail beside gift shops you can put there the either not covered at Tanger or Branson Landing.
I can think of a few outlet type stores that could either come back or make a debut in Branson like Columbia, Woolrich, Mossy Oak, Off Fifth (Saks) relocate Nautica, Pendleton and Carters, ect, ect, ect. Maybe a Cabela's?
What I do know is that it makes me sick to see Oz Cat sitting idle. Being from Memphis, I loved the Zippin Pippin, Elvis' favorite woodie rollercoaster. It nearly rotted completely away when LibertyLand bit the dust but it has reappeared in Wisconsin. Still should be in Memphis somewhere. I find it interesting that I rode the woodie at what was Circus Circus down in FLA when it was Boardwalk and Baseball. It's now at Magic Springs in Hot Springs.