A MaXair/Delirium style would be out of this world; there is nothing like being "upside-down" 180ft in the air. I would really hope that Worlds of Fun would save up for a full-size model, but then again, they could probably build a new roller coaster for the same price. MaXair terrifies me at night, when the ground seems so much further away than it is, and being right on the midway, the tiny little people below don't help things at all.
I still think a nice little family terrain coaster, that ducks into the woods near autobahn, would be a nice addition to the center of the park. Keeping in line with Prowler, try and keep as many trees as possible!