Knowing how much time you have for the duration of the trip helps us in our recommendations . . . If you have 2 weeks or 1 week?

Looking at your list, Colorado in general is a great place to spend time relaxing. Aspen, yes, and Durango, etc. have the slower tempo that MAKES a person relax.

What about flying into either Seattle or Vancouver (often the tickets or vouchers include Canada) and take the ferry over to Victoria, BC. It's a taste of England in North America. Stay at the Empress Hotel if you can - or a B&B but do have High Tea at the Empress. Buchart Gardens are amazing as well.

Places to which I traveled in my 20's and enjoyed:

Miami and/or Key West - can be fun/relaxing. The drive from Miami to the Keys is quite nice.
Las Vegas - obvious for party reasons, but the pools at some of the hotels can provide some major relaxation.
New Orleans - party central, wasn't a very relaxing trip for me, though.

I agree with finding a destination that would otherwise be expensive. San Francisco sounds great too.

Have fun!