Enjoying this post everyone. I don’t cycle gear much, tending to get gear that sounds good to me on a limited budget and listen to it for a long time. But sticking with the “greatest hi-end purchase” question, it was buying a pair of Quad ESL 63s a few years ago. I joined AGon in order to buy them and got them from a great seller for a good price. Turning up the volume on these was a revelation. I never knew recorded music could sound that real.
That purchase sent me down the electrostatic road to a pair of Sound Lab M1s and a pair of MC2500s bridged for 1000 watts. (The SLs are hungry.) All bought used. My wife, a singer, after listening for an afternoon, thanked me for buying them.