I run a fair amount of wood through my Delta 12" planer. It's near 30 years old. Most of my tools are that old, from back when I built my house, though I have made a few additions over the years. The planer is still running, but it needs attention. Just put new blades on it last month. I'd love to get a larger one, or a helical, but it's not a required upgrade. It'd simply make things easier.
I need to reconfigure the space in my basement shop. Picked up a Unisaw at auction not too long ago to replace my cabinet saw, the Unisaw will be wired up during the reconfiguration. Almost bought an old Oliver table saw. I do love old iron. But my working space it a bit tight.
Highly recommend who mentioned a track saw. I've run sheetgoods through the table saw and there were times where my short fence was a frustration when I was making a run of cabinet carcasses. The tracksaw is indeed a game changer, and I find new uses for it.
I guess my upgrade would be different. Better dust collection. I have a regular old 1-1/2hp two bag dust collector with a metal garbage can for the cyclone. I'd love to get a larger one and put it outside the shop space then redo my collection runs inside. It would improve my shop, which would improve me, which hopefully would improve my work!