Looking back over the years I think back and the biggest regret I have was selling a Cyberstorm 060 PPC the PPC did not work for some reason but the 060 was fine.
I also regret throwing out (yes you read correctly) an Amiga 3000T in 1997. it did not work but knowing what I know now it was likely just a bad 3640 card. "Hit head against brick wall"
What regrets do you have regarding getting rid of Amiga items?