For me, it depends on the strength of the hardware upgrades.
I've skipped alternate iPhone upgrades (I owned 3G-4-5S, so far) and haven't decided whether to replace my 5S's battery and wait for iPhone 7, or get a 6S. I'm still using an iPad 2, fer cryin' out loud.
If Watch 2 or 3 is just too awesome to pass up, I'd get one. Or, if my W1 starts to feel long in the tooth, like my iPad 2 does at times, I'll consider an upgrade.
But, I also look at my iPods, the newest of which is three years old, and I realize that there's nothing wrong with them now. They're simple devices with no cameras and no major radio standards to follow -- which is really what the W is, too. Upgrading my iPhone every couple years gets me better cameras, faster LTE, etc., but none of those features are part of the W (at least not with current tech).
So, for now, I'm planning on keeping my SS Watch long enough to have a couple fresh batteries installed. If -- and this is a big if -- Apple offers to upgrade the electronics within the existing chassis (which is the only way the Edition model makes sense to me), I would keep mine a lot longer, too.