Little wonder then that some items (although none of the ones brought up as examples) stay on the market unsold for years...supply can be as scarce as one would like it to be, but the golden rule I learnt here and tried to apply also elsewhere: rarity (or age, for that matter) doesn't mean value - at least beyond a certain threshold.
But if anyone wants to offer me 3000 EUR for my relatively scarce '80s blue box, they'll find me very eager to listen :-D - and surely willing to accept!
Cheers
Fabrizio