The most direct routes would be I-80 or I-70, but not the most interesting.
To avoid all the Chicago mess with a motorhome, consider US 24 from Ft. Wayne to Peoria, IL and take I-39 north to Madison, WI.
From there US 14 into Minnesota. If you want to avoid the metro Minneapolis area, stay on 14 into South Daakota through the capital of Pierre and join I-90 at Wall for the Badland Nat. Park and then on to Mt. Rushmore, Wind Cave, Deadwood and oter Black Hills sites. In Wyoming, leave I-90 for the Devil's Tower.
If you want a little detour,rejoin US 14 at Gillette and then in Sheridan take i-90 north a bit to the Battle of the Little Big Horn(Custer's Last Stand) monument in MT.
If time is then a factor, just turn south on I-90/25 into Denver.
Or, if time allows, take Alt 14 from Daytn, WY over to Cody, WY and the Buffalo Bill Museum before heading into Denver.
Good overnight spots could be Rockford, IL, Mankato, Mn, Wqll, SD, somewhere in the Black Hills (Rapid City Custer, Deadwood)
Cody and Casper.

I'd have to say that Missouri and kansas don't have a whole lot to see and I've done it often, although not as sightseeing, but to just "get to Denver".
If you can see the Black Hills and the Badlands, it would be very good. After that, it sort of depends on what you plan to do in Denver and after that, and how much time you have.
Cheyenne in eastern Wyoming would be good, and then just drop south to Denver.

MO has tons to see, but admittedly not much along I-70. Unless you count KC and St. Louis which I of course do.