My first thougts on Baseball cards and such are this,, I Vintage Mickey Mantle card will always demand it's high value, because it was not made for the "Collectable Market", it was just a cool novelty you'd get in your bubble gum pack at the 5 and dime store. Now come the 80's -90's and People are Collecting stuff and so cards and many other things are made for the collectable market, guess what they aren't collectable as hundreds of thousands if not millions where made.. Simple case of supply and demand..
I laugh every time I see something labeled Collectable.. If it is made to collect it will never be worth more than than the price you paid at walmart for it.
I love this article published in the "Onion" news paper, if not familiar with the onion, it's a satire publication which is in print and online.
http://www.theonion.com/articles/everything-in-entire-world-now-collectible,1508/Now regarding soda machines, I think the vintage machines will always hold value, the Vendo 81's, and such... anyone who appreciates history and likes soda machines will always have a place for one in a collection... Just like Car guys , I"m talking big time collectors who collect 60's and 70's era muscle cars,, most of them have a 1930's Model T or sedan in the collection too...
I'm sure square tops will become more popular, but don't think they'll ever reach the value mark of what a restored V81 brings (avg $6,000) but even if they do I'm sure those collectors would still appreciate and older V81 or something like that...
so here is to the future of soda machines!