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
It took a long time before I felt a need to improve my PC's performance again after that.