There is plenty of room for the NBL to grow. As long as clubs keep improving off the court and improve their connection to local grass roots and their communities then the NBL will see some success. And as long as clubs think big and aim for bigger arenas, bigger membership and bigger crowds - then success will follow.
The NBL operates on a shoe string budget, whereas the A-league (nbl's closest competitor) receives millions, spends millions, and loses millions and at the end of the day, their attendances are only double the nbls crowds on average. Both leagues crowd averages are inflated with Melbourne Victory and Perth Wildcats getting exceptionally high crowds in their respective leagues.
The gap between the leagues might seem large from the numbers and from a perception point of view, but the A-league is only a few big stuff ups away from being like the nbl was/is. And the NBL is only a few good decisions away from closing the gap.
A Brisbane and 2nd Melbourne team or Wellington side is desparately needed.