We're from Kansas City ('burbs, actually), and have made the drive out I-70 from here to Denver several times. Actually, the Kansas Cosmosphere in Hutchison, KS, is supposed to be really cool; it's affiliated with the Smithsonian, even - but I can never get my husband to stop!
The Montana Mike's Steakhouses are really good (there's one in Lawrence, Hays, Colby, and Dodge City. Then there's Dodge City itself, the real deal from the days of Wyatt Earp! From St. Louis to KC along I-70, you should stop in Rocheport for lunch at Les Bourgeois in Rocheport, our favorite winery!
It IS desperately hot along the I-70 corridor, and terribly boring, especially in August, but the Wind Farms are eerily beautiful, and you might get to see the giant fields of sunflowers in bloom - they're quite breathtaking. We always take books on "cd" and listen to pass the time. Have great trip!!!