Get a rental RV there are plenty of places in Denver and it will be more comfortable as you can stop and rest wherever you want!!

Given your limited time and the emphasis on FOF and Glen Eyrie, you don't have much flexibility for other sites. Aspen is not my favorite town -Vail is much nicer - and the only fabulous excursion in the area is to the Maroon Bells (by bus unless you go very early ).S ince you are not hiking, that would take no more than two hours RT. Other options in the area include jeep tours that can offer you some nice scenery. Independence Pass is fabulous but very scary for most folks, as is Trail Ridge Road. You could easily do a loop from Aspen over to I -70 through Glenwood Canyon , with a stop for lunch at Vail and then take the scenic route from Black Hawk through Nederland to RMNP. That would make for a very scenic drive. And RMNP has lots to see from the car.

wow; there are countless excursions in the Aspen area, including Redstone, Basalt, Carbondale, Marble, Conundrum, Castle Creek. In addition, it's a lovely Victorian mining town, compared to a fake Vail. Neither Trail Ridge nor Independence Pass is "scary for most folks"; the views on either are spectacular, and well worth driving. IMO, of course.