I used to live in Denver and ride the Cherry Creek Trail, usually between 6th Ave. and downtown, but sometimes out to Colorado Blvd. In my experience, it was pretty well-maintained, and I was rarely in a situation that required studded tires (at least on the trail.) In some cases, the ramps would be a bit hairy.
That was a decade ago, though, so more recent reports would probably be helpful. That said, I cannot imagine that maintenance has gotten worse over the years.