dry hopping at room temp is fine but did not do a whole lot for me. I think I like dry hopping cold about as much. I guess you might get a more intense initial hop blast but over the long term I think doing it cold might yield smoother results.
also - leaving kegs in the upper 60s for extended periods doesn't do much to help the beer in my opinion. nothing too major but it def aged it a little more than I have experienced if I keep them cold, cold cold.