We also live in Colorado and have been to Wilderness on Wheels. It was a great activity and allowed my sons to participate in a family hike. We also have found several destinations that are handicapped friendly. Mesa Verde National Park has 2 trails that are completely accessible. They allow those in wheelchairs to go right up to the ruins. One of the trails is a little steep, so plan on a little assistance pushing at the top of the hill. We've also been to the Grand Canyon (great accessibility) and San Diego this past summer. San Diego is great!
I found a book called 101 Accessible Vacations, you may want to get the book if you are interested in traveling.