The last time the NBA expanded was in 1980 when it added a franchise in Dallas. It was a good move because Dallas was obviously a very active, young, and enthusiastic city that had the facilities and the sports fans to support an NBA team. The current set of expansions aren't as clear in how they will turn out. Problems with building arenas and questions about personnel and potential fan support seem to be more prevalent now than they were in 1980. The league has been on a high for the past several years as league attendance records have been set every year for the past five.
Television ratings are also very high.
Many NBA teams actually made money last year, a rarity for sports franchises. Things appear ready for expansion, but I have my doubts. First, and most obviously, there is the problem with finding more quality players, especially at the center position where roughly half of the current teams are looking to improve on their situation at the position. Eventually, the problems with finding quality players should work themselves out because they always seem to do so and because more kids will recognize the greater opportunity and will work harder to become good. But, all 27 teams most likely won't be around long enough to see the increased talent flow.