On MLB TV today, Harold Reynolds and Dan Plesac (I think) were talking about Rafael Betancourt pitching, and mentioned how hard it is for pitchers because of the altitude and vastness of field.
Plesac talked about how he heard the hardest thing for pitchers he learned from the Rockies pitching coach Apadaca is recovering from starts. He says because of the fatigue of the area pitchers had lighter workouts in Coors than when on the road. This recovery made it hard to pitch consistently on a high physical level.
They also stated how it is very rare to see any pitcher, reliever or starter, have two consecutive good seasons playing at Coors. Legitimate, but something to think about in terms of pitchers in Coors.