Its very difficult to put a value on a great management company and even more specific on the on site manager. These 2 things can really impact the quality of life and the cost down the road. I also forgot to mention the quality of the board......In a lot of cases its hard to know these things, but if its a building you work religiously, you just get to know them.
I have sold several units in a specific building recently, for record prices well over the comps, as i was able to get this point across to the potential buyers. Some great condos are under priced because not enough people value these things