The nickel finish was discontinued. As it's no longer offered, there will be less of them.
As for value, if it's in good shape, and rare it should retain value better than another model.
However, if it's the shiny nickel as opposed to satin nickel, it is a fragile finish and one scratch will make you want to slit your wrists. Nothing looks worse than a nickel gun with flaking or scratches.
If you plan on carrying the gun, go stainless or blackened stainless.