"Do keep in mind that fully repairing and upgrading an old computer can easily cost more than the original purchase price of that machine. Plus, if you ever want to resell your upgraded machine, there's no guarantee you'll be able to recoup your costs."
This seems like the most worthless piece of advice. An inexpensive Raspberry PI most likely can outperform older computers. The only reason to restore an old computer is if you are a collector, or extremely nostalgic for the days when computers were far less powerful.
Sometimes there is older software that doesn't run on modern computers. Fortunately, your modern computer can run emulation software to emulate almost anything, including older computers.
I could see some 8-bit enthusiasts like myself pining for the old days when computers were very simple. From the standpoint of a computer programmer, those days were fun because the computers were far less complicated; you had access to all the hardware and you didn't have to learn an extremely complex operating system to create a program.