I personally use one public key which I securely synchronise between machines, which can then be added to, and hence access, all the systems I need. In this case, you just have one keypair (two text files) to store. You can put the contents of those files in Excel if you really want to.

By the way - regarding doing this for thirty years, be careful with that as a plea to authority - I read a tweet recently along the lines of "Do you have 30 years experience, or have you just done the same year 30 times?"