Old boardgames do not seem to have the same collecting appeal as
RPG stuff. Most people into boardgames don't seem to care about rare games from the 70s, and prices reflect that.
I have a copy of Imperialism at home (Flying Buffalo, 1974) that was the precursor to Grand Imperialism (Gametime Games, 1978) that I picked up for maybe $10.
Just no interest in the community for older games, maybe because they just want to play the games (unlike here, where people want to collect....)
Demand of them whither they should comme to devide the worlde with the Emperour? And as they answered, he tooke up his shirte behinde and shewed them his buttocks, sayenge unto them, drawe your Lyne throughe the middest of *this* place.