Did this route in 2017 although I would recommend going through Nashville and Memphis instead if you have time to stop for a night or two in each.
St Louis: Of course, The Gateway Arch and Old Courthouse.
Topeka: Brown v Board of Education National Historic Site (map)
Hutchinson, KS (slightly off route): Strataca mine (we didn't have time to visit, but I had it on my list)
Carneiro, KS: Mushroom Rock State Park (map)
Fairview, KS: Garden of Eden (map) also didn't have time for this
Then it's a whole lot of not-too-much until you get to Denver. On the plus side I recall the speed limit here was 85mph.