The one component that you wish you had not bought

VPI PLC  (aka imo - complicated light dimmer switch)

I can't believe even today I still see these things for sale at $250.  

I'm with Mr. Tracy, saved up my pennies ,at a time I didn't have many, to buy a Crown IC-150.
After about a week reality set in and I realized my little Sansui 40watt integrated was VASTLY better !

My Meridian surround sound system, with processor, separate amp, and dsp speakers. I could never get it to sound nearly as good as my 2 channel system. I got better results with a Marantz receiver and non-Meridian speakers, at 10% of the cost. I will never go down the high end home theater rabbit hole again. Depreciation with HT components is much worse than quality 2 channel components.

Oh and I almost forgot my Supratek Syrah! Read all the online hype and what an epic piece of crap, I was rid of it within a week. Poor build quality and didn't sound great either.

Re the Crown IC150.  I never owned one, fortunately for me, but it was notorious back in the 70s for great measurements and lousy sound. It was also unreliable, IIRC. Similarly, Julian Hirsch was notorious among audio cognoscenti for worthless BS reviews; his opinions were based pretty much only on measured specs, obtained in the "Hirsch Lab". Do you recall the Phase Linear amplifiers, with .0000000001% THD?  Got down that low by the NFB method.