I think you don't want to miss Maroon Bells, Rocky

Mountain NP, Royal George Bridge and Garden of the Gods.Great Sand Dunes NP.So if I were you, the plan will be:
Friday: stay in Denver downtown, enjoy night scene.
Saturday: RMNP, Winter Park, Gleenwood Spring, try spa at night.
Sunday: Maroon Bells, drive on some scenic roads, Garden of the Gods, stay in Colorado Spring at night
Monday: Royal George Bridge,train ride if you want. I have no idea about which one is better. Stay a place close to Sand Dunes NP.
Tuesday:Sand Dunes NP, back to home.

You can take a look on my blog. I have some pictures about Maroon Bells and RMNP.

Have fun.