Impossible to forecast what the future will hold for anything - whether it be collector cars or vintage audio gear.
Broadly speaking, objects that were either top-of-the-line, unique/unusual (in a positive way) and/or very popular in their day - tend to be the best bets for collectibility and appreciation over the long term. Rarity and especially condition are important factors as well.
Broadly speaking, objects that were either top-of-the-line, unique/unusual (in a positive way) and/or very popular in their day - tend to be the best bets for collectibility and appreciation over the long term. Rarity and especially condition are important factors as well.

Yes that too.