I think you have done an excellent job and have an amazing and exciting trip to look forward to. I would be tempted to add an extra day between Mesa Verde and Zion as you could easily spend a day and a half around Moab for Arches and Canyonlands and the same in Zion. Between Arches and Bryce is Capitol Reef NP and the drive along UT24 and scenic Byway 12 is spectacular !

From Denver to Mesa Verde you could also drive the amazing 'Million dollar Highway' [US550] through the mountain towns of Ouray and Silverton. To get there you would take US285 to Poncha Springs and US50 which is also a lovely drive over Monarch Pass, through Currecanti National Recreation area and past Black canyon of the Gunnison. It would add a couple of hours to your journey to MV although you could stop short in Durango for the night. If you had the time you could also 'Splurge' on a wonderful steam train ride to Silverton.