Choose wisely. I happily upgraded my system right before and after retiring. Both were upgrades and musical with more tubes. One thing you really don’t want to do is make your system more flashy sounding (I’m thinking Luxman as an example)… make you focus your attention on the system. That is great when you are working because you have only a small amount of time to listen. But after retirement you may have more time, it’s likely you want the music to be pulling you to your system. You probably will want your system more musical. It would be easy to run away from tubes and find you also don’t want to listen to the music.
I have nearly fifty tubes in my system. They require changing every 3,000 hours. That’s over three years. If you have a spare pair your set for six years… that’s a long time. Maybe wait until you retire and start listening and determine your actual fiscal situation. I was extremely conservative the first couple years and then happily realized I could do the biggest upgrade I ever did. I could not be happier. I have to drag myself away from my system after listening for two or three hours each day.