Took me a while to read through this thread, but I wanted to add my thoughts.
I highly recommend everyone try buying and selling on the used market. I've been building custom PCs and flipping them for some time now, and it's really given me a different perspective on upgrading my own rig. You don't have to "time" your upgrade since you have the freedom to sell your current hardware and make back a decent chunk of your investment. After all, that's what all these expensive parts are, right?
AMD really shines right now with the AM4 platform. It supports og Zen all the way through Zen 3 this year and possibly Zen 4 next year. Though specific CPU support will vary by the chosen board (B450, X370 etc.), you have a lot more freedom than Intel offers. Their 2nd/3rd gens shared a socket, but then gens 4+5 shared a different one, then 6+7 and 8+9. Surprising no one, 10th gen is on LGA-1200, so no motherboard you have now will support those CPUs.
You THINK that you're happy with 4c/4t, but that's because you haven't seen what a difference 4/8 or 6/12 can make. It the 1% lows and general system responsiveness that just plain makes the experience better. I've built and sold a lot of PCs now with Intel gens 1-6, and the non-HT systems were pretty stuttery during my testing. I stopped flipping them because I really don't enjoy selling PCs that feel so outdated.
I recommend that if you have a 4/4 CPU or any Intel setup older than 4th gen, you should buy yourself a Ryzen 1600 AF in a B450 motherboard. This combo will run you roughly $160, and then $60 for 16GB of DDR4 (at least 3000MHz) if you don't already have that. The AF model is essentially a 2600 in disguise, so it's a huge bargain. I have one on the way for a new flip build and I'm really looking forward to testing it.
So now you've dropped $220+ tax...BUT you have this older CPU/motherboard combo and maybe some RAM to sell. If you scout your local market using Facebook Marketplace, OfferUp, Letgo and so on, you'll likely find that you can get at least $100. Some people want to build a basic gaming PC for Fortnite, WoW or Minecraft and simply won't care that it can't handle Cyberpunk or GTA6. Maybe it's a dad gifting his 8yr old, or a non-gamer looking to build a cheap home server. Whatever the case, selling your old parts just cut your upgrade cost in half!
You can argue all day long whether 6/12 will "last you" for five years, but you have to break this mentality that you're stuck with anything you buy! You'll have an upgrade path to Zen 3, and even if your board ends up not supporting it, a bunch of Zen 2 CPUs will hit the used market and you can pick up a 3700/3900 at a substantial discount.