Mass produced goods generally don't appreciate in value. When it comes to guitars and basses, make no mistake - Fender today is a mass market brand. The thing about early Fenders is they didn't make very many of them - those of us who were around in the 60's remember that seeing someone playing an electric instrument was a pretty rare event, except maybe on TV - there just aren't that many of them. There are enough people with nostalgia for such things, and who have enough money, that early Fenders today command a decent price.
Fenders made more recently are present in much greater numbers. Apply the law of supply and demand, and you can pretty easily figure out that a recently made Fender is unlikely to command a high price a couple decades from now - unless the market for them increases greatly. That probably won't happen. Fender makes decent musical instruments nowadays (better than the early ones in most cases). They aren't good investments, though.
Fenders made more recently are present in much greater numbers. Apply the law of supply and demand, and you can pretty easily figure out that a recently made Fender is unlikely to command a high price a couple decades from now - unless the market for them increases greatly. That probably won't happen. Fender makes decent musical instruments nowadays (better than the early ones in most cases). They aren't good investments, though.