Should I refresh every old computer I work on? Probably.
However I think that if a computer works and can do the tasks that you need it to do, just leave it alone.
This old Macbook has been backed up and I removed a bunch of software from it that is outdated or no longer working. Seems fine. I think I'll just leave it as a writing machine - one that is distraction free because trying to run a Google Search on it takes longer than it does to make a cup of coffee in the Keurig. A big cup.