I think we're going to start thinking about the watch and band sets the way SLR photographers think about bodies and lenses.
Typical camera body is $1000-$5000, but you acquire a whole set of attachable lenses that run anywhere from $500 to several thousand dollars. The lenses typically have mounts and connections that are kept stable for many years, so the photographer will upgrade the body every few years to get the latest tech (autofocus, sensitivity, software), but the "glass" collection will keep its value over time even though it's never upgraded.
Years from now, I think we'll see there is still a market for used link bracelets; Apple may have come out with totally different designs by then, equally interesting and at similar price points, with the same connection mechanism.
I think where the big departure may occur is if Apple builds some electronics into the bracelets themselves that require both new watches and bracelets. But even then, like my SLR analogy, the old bracelets will likely still physically attach, you just won't get the extra sensor data.
