Deacon had a good response to this on the Bladeforums. I've stolen it for here:
As for whether a CC# adds value, I'd say no in almost all cases. A "matched set" of all the variants of a given knife with identical numbers "might" be worth a premium, but aside from that no. Especially on the newer models where backlogs in the engraving department mean the CC# can no longer be taken as indicating the knife was one of the first 200 produced.
On the other hand, carrying a numbered knife does have the advantage of making the knife identifiable if lost or stolen. There may be a lot of Enduras in the world, but there's only one Endura 4 with that exact combination of features (handle material / color / steel / edge) and 061V engraved on the blade.
“Open, close, cut, clean, oil, cut, cut, cut... To a Spyderco, that is living. Letting it die in the box is to lose 75% of what we put into it." -----Sal Glesser