I'd rather see the station fufill it's intended purpose of being the nexus of mass transit in the front range for another 100 years than let it just be abandoned and cast aside like so many other stations. We will be losing one of the most photogenic passenger train stops in the state. But we will gain more passenger trains in the end.
As for smoke, since it must allow idling diesels I bet steamers will work just fine as well with some banking of the fires.
I imagine the 20th street will be moved from an underpass to surface level, and the train will run below that, so the tracks will not see daylight until they are behind Coors Field at the start of the wye between North Yard and the UP/BNSF connection.
With the need to accomodate Amtrack superliners this may be a pretty deep hole they are digging.