I know you will have just completed the special Eng/Fireman school on the C&TS and might be burned out, but you did say "Railfan Advice" in your title. With the limited amount of time I would do this.
Thursday morning sleep in till about 8
--Chase regular Passenger train to Cumbres (10-11:15 ish)
--After Cumbres drive back to Chama, then Pagosa Springs to Durango
--Drive to Rockwood and catch the return from Silverton at the Cut
--Chase one of the last ones back to Durango selecting a few nice spots.
So for Thursday you have seen at least 3-4 different Steam engines.
Friday Ride the D&S and relax to Silverton. If you want to get out of dodge early, you can ride it one way, bus return.
You can always chase the first train or two instead, but the ride is nice along the river. After your ride, or chase, you can drive toward Denver.
--Saturday do your stuff you wanted to do in the area around the crowded metropolis of the big city.
Greg Scholl
PS You really need a separate trip to do all the old right of way stuff.
Someday if the C&TS or D&S is not running there will be time for sight seeing. That was always my logic with Europe and foreign travel. I can always go back and see the tourist sights when the steam is gone. But thats just me!!