Just returned from a 2000 mile round trip from northern Colorado to the Grand Canyon, so I now have a renewed perspective on some of the locations mentioned above. Though I've been through these areas many times in the past, having a new view gives a new enduring love of those areas.
I agree that, for a good overview of Colorado, choose the Upper Arkansas River Valley area of Salida/Buena Vista/Leadville. Many good places to set up a base camp and then explore outward from that base camp. The Collegiate Range of mountains is a formidable collection of 14'ers, with magnificent views from anywhere in the valley. And lots of trails and roads to explore. Day trip to the San Luis Valley? Easy. Want to head to places like Glenwood Springs? Done. Aspen? Just a trip over one of the highest passes in Colorado with views that are unbelievable. If you're getting brouchures in the mail, start with those that are within driving distance of this wonderful area for a base camp. You won't regret it.