I think this is the nicest New Standard I've seen in decades! No visible dents and the satin silver finish is "worn less than 2%" according to the seller. This is the large-receiver era. It includes a new hard case (MTS, I think).
The buy-it-now price is $3,950. I suspect you won't find one in this condition for less, but that's only because you never see one in this condition. Is it worth it? I really don't know. The quality and character of these horns are terrific. The new case would help you keep in in its current condition. Here is a recording of my playing the same model in 1978: https://www.youtube.com/watch?v=KGNE6WtAOdg (I was using a Bach 5G at the time.)
http://www.ebay.com/itm/BESSON-NEW-STANDARD-4-VALVE-COMPENSATING-EUPHONIUM-NO-DENTS-MADE-IN-ENGLAND-/261932861715