As beautiful as Telluride is, I would skip it this trip. You are doing more driving than stopping to smell the roses. Stick with places further north than driving so far south to Telluride.

I'm not from Colorado but I have been most of the places you mention. My thought is that you will be shocked with the drop off fee if you rent at Denver airport and drop off in Utah.
The California Zephyr leaves Denver every morning and has stops in Winter Park (Fraser), Glenwood Springs, Grand Junction and SLC. The drawback to SLC is that the train arrives very early in the morning.
Aspen is only 41 miles from Glenwood Springs and there is a great bus service between the two (RFTD).
Glenwood Springs has two old historic hotels within walking distance of the Amtrak station. Near the hotels is the world's largest hot spring fed swimming pool.
You might want to get off the train in Grand Junction and rent a car there for your trip into Utah. In any case, plan on returning the rental car where you rent it.

Thanks for the tip about Telluride. That was my inclination and wondered if I am trying to see too much. It does look really nice though. What other place if I stay north would you recommend? I anticipate I will be taking I-70 into Utah.

As for the car rental drop fees, I actually got a great deal through Costco travel and booked 3 months ago. If you look now, the rates are through the roof.

Thoughts on staying in Vail or Glenwood Springs for a couple?

If you are determined to take 70 to Utah, do drop down and at least do a drive through in Arches and Canyonlands Island in the Sky district.

I would drive on through RMNP and then drop down to I70 to head west.

This the place to stay in Glenwood Springs. http://hotelcolorado.com/
Enjoy some time in the famous swimming pool.

Sounds like too much driving.

Getting from RMNP to Aspen will be circuitous. The scenic route would be to drive over Trail Ridge Road and exit the Park at Grand Lake. Stop at Grand Lake Lodge for lunch.

Take this route, which will connect you to I-70 West, taking you through some pretty and open Colorado country.
http://www.distancebetweencities.net/grand-lake_co_and_aspen_co/route

Once at I-70 West, you will go to Vail, then on to Glenwood Springs and Aspen.

I was viewing the maps and it seemed like I-70 was the better route to take into Utah to see some of the sites. I -40 took me into where my final place with be, Park City, but didn't think I would see as many places along that route.

I was also reading I should see Black Hawk, Dillon, Idaho Springs. Too many places to consider. Are these places worth the visit for a short time?

As i wrote above, if you drive through RMNP you come to Route 9 south to get back down to I70 at Silverthorne/Dillon/Breckenridge/Keystone (if you want to go a little off the interstate). Then you are less than an hour from Vail at Silverthorne.
Idaho Springs is east of Silverthorne, and a cute little town, but you won't miss too much. Just go to the park and through it.