It happens with all cars or trucks eventually from 1970 Cuda's to 1967 VW Beetles. The worth is denied and tons of good examples are destroyed.  Next thing you know you cannot find any clean stock examples left. Take the early VW bugs people you to think those would be around forever after all they made tons of them. My friend mark in 1991 bought a mint Black on Red 1967 VW with only 22K original documented miles it came with every sheet of paper from it's birth. Plus a few "real" Empi / Speedwell parts he paid $7500 for it and people told him he was high for paying that much for a bug, in 2006 he sold it for $45k to a Japanese collector.


Right now in my opinion the 79-85 trucks are at the balancing point where there is hardly any clean examples left. I'm asked nearly weekly if I want to sell my 85, and most people but up a straw man argument about the ones they can buy off uncle John's farm for $1k to justify their insulting offers for mine.
It's really hard to say where the prices of these early trucks will go, but I don't see it heading down that is for sure.