Kansas City to Metropolis, IL, special just for Bob. It'll be visit number three for me, but I reckon that we might be inclined to take the tour at the town gift shop's crazy museum with Bob along. It'll take about 7 hours to get there, ignoring any time stopped for lunch and the like.
Metropolis, IL to Cincy, another 7 hours. This route takes us through Elizabethtown, around Louisville, and on up into Cincy from the south. It might be in our best interest to get a crappy motel on the Kentucky side of the stateline since we're looking for somewhere on the cheap side.
Kansas City to Cincy, direct. Google pegs it at just short of 11 hours. There isn't much along the basic route of interest aside from your usual random highway oddities (like the ginormous cross that I believe is along the highway in Indiana). The biggest downside to this route is the fact that there isn't any reason to get to Cincy so quick. Maybe we hit the Arch in St. Louis (I've never actually been)?
I don't really have a third route. I've been searching for someplace between here and there that might be worth hitting, but nothing really stands out that isn't horribly out of the way. We could take a minor Sufjan Stevens tour of Illinoise (Godfrey, Highland, Jacksonville, Mt. Pulaski, Decatur, Metropolis, etc.), but that might be much too nerdcore, even for me. We could always meander as well and just bounce about. I have a soft spot for wandering through tiny towns by way of state highways...
I'm partial to Route A, not only because of the visit to Metropolis, but because Kentucky is pretty country to drive through, even if the people are a little backwards and scary.
EDIT: I just read that they're having a Superman Festival from June 8th to the 11th. We might want to consider making our visit there on Sunday instead, which brings us back to having no real gameplan for the trip there.
Edit 2: For Bob: Jen's wedding page so you can get the address of where the wedding and reception are at, if it should help in hotel hunting.