I don't know about the value, but as far as the dating goes, I know that Stubben made their saddles with suede knee pads until 1994, or so I was told. Also, I have heard that the green nailheads are for saddles made in or after 1985, and the silver ones are for pre-1985. You used to be able to contact Stubben with the serial number and they could give you a date of manufacture, but I'm not sure if that's an available feature anymore. I contacted Courbette (I believe them and Stubben are paired now) about my saddle and they gave me a date for it, as well as some information about it, like what kind of tree it has and that my specific model was discontinued many years ago.
I think on some models the last two digits of the serial number may be the last two digits of the year of manufacture, depending on which factory it was made in. Mine are 80, and my saddle was made in 1980 in Switzerland.