I'll be there! I've done RTR almost every year since 1993.
I've not ridden the dirt section in question, but the other dirt roads they've used in the past have actually been smoother than most of the pavement. They spray some kind of chemical binder on the road ahead of time.
Colorado pavement, especially in the mountains, is pretty crappy. I wouldn't use anything narrower than 32mm myself.
Having said that, 90+% of the riders use skinny 23mm tires and seem to enjoy themselves. You do see lots of thick bar tape, jelly filled gloves and those anti-vibration bar plugs!
On one particularly rough section I once picked up almost a dozen of those plugs that had rattled loose and fallen on the road.
I'll be on my 650B Kogswell with 38-40mm tires, probably Trimlines. Fenders too.
I'll be surprised if there are more than 10 fendered bikes there. I've seen many totally rain-free years, but last year, it rained like hell on the last day. You never know. Most likely, rain will come in the form of the occasional brief, but intense afternoon thunderstorm.
Also, a bell is worth it's weight in gold when sharing the road with 2000 other riders.
Ryan in Albuquerque