Since you have expressed some specific interests, here's some additional ideas while you are in Colorado:
1 - The South Park area, specifically Fairplay and Alma. In Fairplay, there's South Park City, a recreation of the old west, with a collection of buildings that were moved there from other locations in South Park. Authentic and as western as you can get, IIRC they've also had movies/TV shows filmed there.
2 - Canon City/Royal Gorge area. While severely damaged by fires a couple seasons back, the Royal Gorge area is quite beautiful. The bridge itself wasn't damaged, and there's been a lot of rebuilding going on. There's a tramway to the bottom of the gorge and a train that runs through the gorge that are fun to see/do.
3 - In Manitou Springs/Colorado Springs area there's a tremendous choice of things to see/do. There's the Pike's Peak Cog Railway. Seven Falls. Cheyenne Mountain Zoo. Will Rogers Shrine. Garden of the Gods. Air Force Academy. Olympic Training Site. LOTS of museums.
3 - In southern Colorado, I'd highly recommend the Cumbres & Toltec Railroad tour, starting in Either Chama NM or Antonito CO (can start at either point on the train, and take a bus back to start point). There's also variations such as half trips from either point. My personal preference is to start in Antonito CO, since it's high desert area, and watch the gradual scenery change as one gets to higher elevations. It straddles and crosses the CO/NM border many times as it gets into alpine territory, stops for lunch at Osier, and then drops down dramatically into Chama NM. There's a thread on here about camping in Chama NM, and one can also start the trip there, or grab the bus there and go to Antonito to start. Either way, it's a must see/do experience!
4 - Mesa Verde/Durango/Cortez. I'd also recommend the Silverton & Durango Railroad while you're down in the 4 Corners/Mesa Verde area. Lots to see and do around Durango and Cortez. Just walking around town in both is a fun way to spend the day. Old West museums in both towns. Mesa Verde could be a camping destination if you'd like, you can camp inside the park. There's also the Canyon of the Ancients National Monument outside of Cortez. A trip down to the 4 Corners monument is a fun day trip.
4 - You've got Denver on your list and there's a whole lot to see and do there, depending on where your interests take you. Couple of places that might interest you -- The Colorado School of Mines Museum on it's campus in Golden; lots of mining historical information, and a collection of moon rocks. Colorado Railroad Museum is also in Golden. Coors Brewery tour, if you're into that sort of thing, also in Golden. Several good State Parks in the area to stay at, as well as some good CG in the Golden area, including Chief Hosa Lodge and CG, the oldest CG in the United States.
That's just the tip of the iceberg for some of the things to see/do in Colorado!