I look at old Weaver scopes a lot like I look at old Parker shotguns, they’re not all valuable just due to the name. There were different levels of quality, even within the same model.
Most of the Weaver K4 and K6 scopes I’ve encountered, I wouldn’t give $20 for. Not because they are bad scopes in general but because the particular scope I was looking at wasn’t worth much.
Weaver is a historical name in American optics but there’s a tendency for sellers to ask high prices based solely on that name. There’s also a LOT of nostalgia surrounding the old steel tube K4 and K6 models that tends to exaggerate the alleged quality more than reality. In simple terms, just because it’s old doesn’t mean it’s good.
I like fixed power scopes and the old K4 & K6 Weavers were classic American fixed power scopes. However, more often than not, I would give more money for an old Leupold than I would for an old Weaver.