I regret nothing, over 40 years of buying hi fi. Why? Because you learn every time; of course you still make mistakes, but hopefully they are different ones. You can't engage in this hobby without a few risks, that is part of the fun.
Item I most disliked/sold most swiftly? A Chord 1200 amp. It could strip wallpaper from 90 feet.
My only regret: Naim 01 tuner.
Lovely device, but with much angst & sadness I took two years to learn the local FM signal isn't up to standard.