NolaKaty

With the time you have I think SW CO and NW NM would be a lovely addition. We are doing NM this year and our trip to Colorado that got moved around a bit originally included Durango and Ouray which we will definitely do another time.

For the Aspen area we stayed in Twin Lakes in September and it was literally the best vacation experience of our lives. We did day trip to Aspen and Leadville as Twin Lakes is centrally located. The grocery was not far for a beautifully scenic ride to Buena Vista. This is where we stayed:
http://www.mount-elbert.com/barn.htm

If you do Manitou Springs, I think you could do it in about 2-3 days. We spent 4 days there and really didn't need that much time to see the things we wanted to see. I wish we had spent more time in the Aspen area.

irishswampyankee

Certainly do Mesa Verde. Then, the Million Dollar Highway area north of Durango is gorgeous and Ouray and Silverton are pretty towns, lots of mts and hiking. However, IMO, while the RR trip might be fun, I would drive the rd instead. You don't want to do both (repetitive) and driving would give you more flexibility. You could stay in Ouray or Silverton, do your thing there, then drive up through Telluride, Crested Butte, Breckenridge. Then decide if you want to head south to return to Dallas or car pickup place or continue on to Rocky Mt Natl Park and Denver.

As others have said, CO is beautiful but very different in summer than winter. Enjoy.