What Product Did You Overspend On?

The biggest mistake in my audio life was to NOT buy piles and piles of NOS tubes back in the 1970s!! (a garage packed solid with Telefunken, Mullard, Western Electric RCA, etc audio tubes.. would have been very nice.)
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Then the next biggest mistake (around 1986?) to trade in a Hafler Dh110 I had built myself from a kit, to buy a POS Sony Digital Preamp. The very first digital preamp with all sorts of fancy adjustable doodads. Well, after the 'new' wore off, I stopped listening to music.
Eventually i realized it was the Sony preamp. I had just loved listening to the Hafler setup .So I sold that POS Sony and bought a nice Counterpoint preamp. Which was also a lovely sounding preamp. (too bad it kept breaking down!!)
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Recently the only mistake (though it cost me nothing, as i was able to return it to the dealer) was accepting the accolades over a particular DAC that was raved about in the magazines. i bought it along with an amp. preamp, and speakers. Well the DAC disappointed me, as my OLD DAC, sounded just as good. i tried every which way to find if some error i was making.. finally i returned it.
My error was to actually believe the hype about a product i did not audition. (all the other stuff i got to audition.)

Although I didn't overspend on this item, I was thoroughly disappointed with the Oppo BDP-83. I know it gets/got great reviews, but the midrange sounded very "thin" to me, and after a couple of weeks, I sold it. This was a used machine, not a new one, so I doubt it needed any breaking-in.

I purchased a pair of Musical Fidelity 550Ks for half price after they were discontinued -- $2500.00 for the pair -- thinking it was an inexpensive (relatively speaking) way to get a pair of high-end, high-power monoblocks (I never bought into the "supercharger" thing and never used them that way). Big mistake. They have the most brittle, gritty high-end I've ever experienced in an amplifier, and they now sit in a corner of my listening room collecting dust. I don't even feel I can sell them, in good faith, for anything other than a P.A. or similar application. So there they sit.

My confession....

In 1997 I paid full boat for a Bose Wave Radio with a cd attached on top. I hated it from the first second, and I never felt better about it. Ever.

I think that the question that you are asking is quite confusing. I only purchase used gear and when I am looking for something specific that is either made in small quantities, or is in demand, I am happy to overspend on it. Even by paying over market, I get what I want.

That is quite different than buying a disappointing product. In a real sense, no matter what you pay for a disappointing product it is too much.