What would it take to make you upgrade?
A different style Watch, preferably round. Seriously, I really like my current Watches and can't think of anything I'd want different other than the inevitable speed/battery/thinness tweaks. wOS3 made the Watch even more useful and I think software upgrades will be enough for me.
Apple performs far more incremental than major upgrades on their computers, so I tend to keep mine for a very long time until something pretty major comes along.
I view the Watch in the same light. GPS doesn't mean much to me. Phone calls? I have a phone. Battery life is doable. Speed could be better.It will get a little better than wOS3, but not much. And that doesn't bother me.
I'd like an iPad iOS Watch that could be verified by my phone so I had more room to use the My Watch section. I'd like more watch faces. All software stuff. Without a style/color change, I'm good. Even if I did upgrade, I don't see me taking any Watch out of rotation.