Between Omaha and Lincoln, the US Air Force has it's Strategic Air Command museum. Just walking in the door, you are greeted by an SR-71!
I didn't like the arch at Kearney, but that's me.
If you stay on the interstate, you might like the Pony Express Museum in Gothenburg.
If you go through North Platte, the Buffalo Bill Historic Ranch on the north edge of town is interesting. Be sure not to miss the rifle stock shaped barn rafters!
You could detour from I-76 and drive through Pawnee National Grassland west of Sterling, CO.
If it was me, I'd get off the interstate...
At Beatrice, you can visit Homestead National Monument.
Minden Nebraska has a great attraction... Pioneer Village Plan on a few hours.
The "most scenic lake in Nebraska" is located north of Cambridge (on US 6 & 34) a few miles. The Medicine Creek State Recreation area would be a nice place for the night. Almost all small Nebraska towns have RV hookups at a bargain if not free.
Depending on your tow vehicle, perhaps a stop in LaJunta would be in order to see the dinosaur tracks...
Dinosaur Tracks in Comanche National Grasslands Picketwire CanyonThere is lots to see along the routes back to Colorado... have a great trip!