Depends on where the bottleneck is.
1. Operating system, potential new update that tanks the performance;
2. CPU;
3. SSD.
RAM is never the bottleneck, unless it is volume, but with modern systems that support north of 128 GB, it is hardly the case.
I only build a new computer when I see that the current performance of my system is too low.
For example, when I had a Core 2 Quad Q9450, some games started to ask for more cores, I got extreme micro-stuttering, as well as another CPU bottleneck.
True, but I see the bottleneck, in my system anyway, as the graphics card. I have an RTX 2070, and a monitor that runs at near 4K (5120x1440) and that's the bottleneck in my system, I have the fastest PCiE 4 SSD on the market and have no issues with waiting for anything. Windows Boots in seconds, much faster boot that AM5.
I'm able to play Cyberpunk with 20 mods that improve detail, draw distance etc as well as a 4K texture pack at 60fps HDR using DLSS quality, and my dream is to be able to play that at native resolution, without DLSS, with path tracing at 60fps, and the 5080 will do that. I know it won't be my CPU that holds it back, as I'm not playing at 1080p or 1440p so my system will still be GPU bound.
The way I see it, yes, a Zen5 9950X3D will offer about 25% more performance, but no games even begin to use 50% of my current 5950x CPU. For instance, Cyberpunk uses about 12-14% of my CPU...
Task manager while playing Cyberpunk...
I'm just not feeling even the slightest that my system is slow or unresponsive. It's lightning fast, and if there were any kind of slowness, I'll reinstall Windows. I work in IT, and see dozens of computers every week, some worse than mine, some with higher specifications than mine, but mine still feels faster because it's not full of corporate crap, 3-year-old drivers, etc. The only aspect my system sucks in, is the GPU. But the RTX30x0 were unobtanium and did not offer enough performance improvements to justify the cost, the 40x0 is not enough of a leap over the 30x0, so I'm waiting for the 50x0 series, as that's now going to be a night and day difference to my ancient 2070. That's where the rubber will hit the road for me, so I can watch AM5 get phased out without crying.