They kind of aren't. If you actually look at "how many dollars am I spending per month on electricity", there's a good chance it's not worth upgrading even if your computer is 10 years old.

Of course this does make some moderate assumptions that it was a solid build in the first place, not a flimsy laptop, not artificially made obsolete/slow, etc. Even then, "install an SSD" and "install more RAM" is most of everything.

Of course, if you are a developer you should avoid doing these things so you won't get encouraged to write crappy programs.