Getting my first SSD was absolutely the best computer upgrade I've ever bought. I didn't even realise how annoying load times were because I was so used to them and coming from C64s and Amigas even spinning rust seemed fairly quick.
It took a long time before I felt a need to improve my PC's performance again after that.
There were quite a few mind blowing upgrades back in the day. The first sound card instead of PC beeper was one of my most memorable moments.
I remember loading up Doom, plugging my shitty earplugs that had a barely long enough cable and hearing the “real” shotgun sound for the first time. Oo-wee
I once had a decade old Thinkpad that suddenly became my new work laptop once more thanks to an SSD. It's a true shame they simply don't make them like this anymore.
I owe much of my career to an SSD. I had a work laptop that I upgraded myself with an 80GB Intel SSD, which was pretty exotic at the time. It was so fast at grepping through code that I could answer colleagues’ questions about the code in nearly real time. It was like having a superpower.