Eh, I buy on a 4-6 year cycle. Here's what I bought:
Phenom II x4 - ~2010
Ryzen 1700 - ~2017
Ryzen 5600 - ~2022/2023
So, ~7 years, then 5-6 years. I had my Phenom II in my NAS until I decided to move my 5600 to a SFF case and put my 1700 in as an upgrade (and it uses less power, so double win). Oh, and I still have that Phenom II and my wife's old 6300 just in case my kids need a PC (they currently use mine).
You really don't need a top of the line CPU for most things. If you go for something mid-range prioritizing cores over clock speed, it'll last a while.
I haven't had any PCIe bottlenecks, everything has been "fast enough," and I upgrade when the CPU starts bottlenecking things. In fact, my GPU still doesn't saturate PCIe 3, much less PCIe 5. So yeah, PCIe improvements aren't high on my personal list of requirements. I'd prefer lower power usage and smaller physical size.