It may also increase the visibility of the league and therefore increase fans and sponsor attention and will also increase the crowd size for those "derbies" because at least there will be more than a handful of traveling fans for once.
Welnix owners have openly said they want a 2nd NZ side in Auckland. If anyone is aware of the pros & cons of another A League team in the NZ market it's them.
A game every week, with potentially double the A League/football media coverage in NZ, are two big pluses. Eden Park would have to be the home ground. Other venues there don't work.