Back when I had a desktop computer (almost 20 years ago!), I would usually keep the case and upgrade motherboard, CPU, RAM, video, etc. Unless the case was holding back something I really wanted to do (like have more drive bays or PCI slots), I'd see no reason to replace the case. In fact, a case upgrade would be independent of the component upgrades. I had a very janky, cheap case for the machine I built for college; once I graduated and had a job and some income, I replaced the case without upgrading any of the components. And then a year or two later I think I upgraded the motherboard and CPU.

I'm pretty happy with the Framework 13 form factor (though, after 3 years of use, I'd still probably prefer a 16:9 or 16:10 screen over the weird 3:2 they ship with), and absent any future catastrophic damage to it, I don't see a reason to replace the chassis.

And I've already upgraded a few things in it: I have a newer mainboard (well, to be fair, I got it due to a warranty repair where they decided it was cheaper for them to upgrade me to the 2023 model), and I upgraded the built-in speakers and the webcam. I'm thinking about upgrading the screen as well at some point. In two years I'll probably replace the mainboard and RAM (not that I want to replace the RAM, but I have DDR4 now, and I'll presumably need DDR5).