From Denver I'd borrow Union Station. Despite it being handicapped as a terminal instead of a through-station in the most recent developments, it is still the coolest transit hub in all of the four cities.
From Colorado Springs I'd like to copy the Pike's Peak cog railway. I know it's not technically in Colorado Springs but it's close enough. I think it's an awesome way to give every person access to the tops of the nearby mountains. Many tall cities have an observation platform at the tops of their tallest buildings, but the mountain peaks in our western cities are taller than even the tallest building on earth, and I don't think we value those views from the top enough.
Boise has the thing I want most though: the greenbelt and river straight through their city. I still can't get over how cool it is that this is happening in their downtown area:
There are very few things that can bring a community together better than a river everyone can swim and boat in.