It is cool and I like it(old thinkpads are awesome) but the slowness would hit me every time I do something a bit more intensive(like browsing the web with hundreds tabs). Maybe it is related to the fact that now I have really fast hardware.
Also it really depends on your use case. I have a VM heavy workflow which benefits from the insane amount of RAM I have in my laptop and the number of cores.
Maybe if you have hundreds of tabs active, but I have literally over 5,000 tabs in Firefox on one of my machines and that's 5 to 10 year old hardware with I think 8GB of RAM.
(Aside: yes, I know I have a problem, but the point is that it works)
Anything later will forcibly shut down after 30 minutes if (at least a fragment of) Intel's closed & bug-ridden monitoring code is not present.
I ran me_cleaner on a few of these systems, and I do all my finances with them running OpenBSD (usually on q9550s).
Yes, this effort to run old hardware is worth it for me. Below are the bios images that I was able to produce: