Both are about a year away, so you're going to have to ask yourself if what you currently have is good enough to keep for another year. Kaby Lake is simply a refresh of Skylake, so I wouldn't expect any major performance increases there, probably some slightly boosted stock clockspeeds and some chipset improvements with newer motherboards perhaps.
As for Zen, we don't know much about it and we'll have no idea how it performs until its actually out. It could be a big improvement that actually makes AMD competitive with Intel again, or it could be another Bulldozer style faceplant that isn't much of an improvement over its predecessor outside of certain specific situations.