Card collectors need to predict the future. When they are investing in vintage graded basketball cards, if they guess that there will be more collectors after those cards in the coming years they can grab some bargains right now. Old basketball cards were a blip on the radar until the early 90s when the market picked up and it's stayed strong ever since.
As the supply of vintage basketball cards is limited, especially those graded at MINT 10, and the popularity of basketball and the number of fans around the world can certainly increase it could mean prices will go up. Throwback jerseys of the NBA's early stars are popular, and video game makers are including past stars in current games, it makes sense that the people who buy those items will begin to look at purchasing graded vintage cards. For many in the 30s, even the rare 1990s insert cards that are so hot right now are 'vintage'. That's the league's core demographic and those people will always be fans and most find the game's history fascinating.
If a couple of high-end collectors decided to go after the few mint condition 1948 Bowman cards and the first Topps and Fleer sets the prices could go up quickly. Baseball player Dmitri Young spent plenty of money acquiring the best baseball rookies, graded Gem Mint PSA 10 (which he later sold), and there are many other sports people and those in the entertainment industry with large bank accounts who could look to basketball cards as a hobby. Another potential new market for high-end vintage cards are international collectors, especially those in Asia.
There is a market for graded cards, for the superstars of the early NBA and even for cards that came before the NBA existed. One example is the small number of basketball cards that were part of the 1933 Sport Kings set. Nat Holman was a famous player in the ABL, and one of his cards sold for $15,880 at a Mile High Card Company auction. Holman's 1933 Sport Kings #3 card was graded PSA 8 NM-MT. An Ed Wachter card from the same set, 1933 Sport Kings #5, and with a grade of PSA 8.5 NM-MT+ was sold in a Memory Lane Inc. auction for $5,053 .
The ESPN 30 For 30 and NFL Films documentaries have shown that sports fans want to learn about past stars. The market for vintage basketball cards could increase with more exposure of the sport's past. The recent documentary about the 1992 Dream Team increased interest in those players with a new generation of fans.
One thing going against possible growth in prices of vintage cards is that many of the teams do not exist in the same manner that they did four or five decades ago. A lot of the best players from the past have rookie cards from relocated and renamed teams, so current fans may not be as enthusiastic when it comes to collecting cards of the Rochester Royals or Syracuse Nationals.
Another possible reason for the vintage card market to stay at its current level and not grow is that the NBA is a league driven more by highlights and player popularity than it is by career numbers and achievements. Dolph Schayes may be a legend of basketball, Sam Jones won ten NBA titles and Jack Sikma won a championship early in his career and even led the NBA in free throw percentage as a center late in his career, but Nate Robinson would have a lot more fans than those players combined due to his Slam Dunk contest wins.
You can the most watched basketball cards on eBay to see which vintage cards might be very popular with collectors, a list that almost always includes some of the game's icons.