This thread makes me sad, as I remember a few nuggets I foolishly tossed out because I couldn't see the use in them then.
A 66 Pontiac Bonneville body and bumpers. It was buried in 30 coats of enamel paint that I didn't know how to remove, but it was intact and I assumed it was similar to the 65 that I already had. A month after I threw it out, I read an article on how to strip paint from plastic.
A "Wild Hoss" 78 Bronco. I had customized it to many times and it too had lots of paint, but I know now I could have stripped it and started over. I still have parts of this one around.
72 "Boondocker" Blazer. Same as above. Since this one has been reissued - it doesn't hurt as much.
Johan 75 Eldorado and 74 Javelin AMX snap kits. Each had a couple chipped pieces that could have easily been fixed.
68 Chevy tow truck. My dad had built this truck twice! One as the pickup (painted dark candy blue) and the tow truck (lime gold). Since I already had the pickup and the tow truck was missing the grille and some other parts, out it went.
I know, I know. Foolish youth!