I still use a 1070, so the GPU comparisons here aren't relevant.
The main issue I hit was deciding between DDR4 and DDR5 RAM since we're in an awkward transition phase - and that affects motherboard and so CPU choices too.
I used to upgrade every generation, and yeah, it was stupidly expensive. But it was my only hobby, and you could actually seen performance increases each time.
But for the last 10 years or so, there's much less point. Sometimes there are major advances (Cuda, RTX) that make it worthwhile for a single generation upgrade, but mostly it's just a few FPS at highest settings. So now I just upgrade every few years.
Back in the 90s and early 00s, frequent upgrades were kind of required to stay up to date with new games. The last 10-15 years have been muuuuch slower in that regard, thanks to consoles I guess. I'm not complaining, but I miss the sense of developers really pushing boundaries like they did in the old days.
Well, I've had the same CPU/Mobo/RAM for over ten years and only upgraded my GPU once from a GTX660 to a 5700xt at the start of the pandemic. I'm finally seeing some issues with some modern AAA content. Hogwarts legacy won't really run at all, for example.
I also haven't wiped my system in the same amount of time, so that may be more the culprit than the system itself. Still going strong!
The CPU becomes the real issue though - which then means changing motherboard, which means changing RAM, etc. and then you might as well get an NVMe too etc.
Sometimes you get around that for longer by upgrading to the highest possible configuration on that platform. Often for cheap second hand.
I replaced my 2017 Ryzen 1800x with a Ryzen 5800x3D recently which is supported on my x370 Motherboard. Huge upgrade, no platform change required. I think I can wait for DDR5 and a new motherboard for years to come.