That's really up to you.
If your current system fits your need, then there's no point upgrading.
My current computer is nearly 10 years old at this point, because even though the CPU is trash by today's standards, I could still play pretty much every games on it just by changing the GPU.
Yes Zen2 is much better than your first gen, but is there any pressing reason you need to upgrade? Other than having money burning a hole in your wallet?
You could easily do another year with it, for when Zen2+ is released.