I haven't lived in NZ for a few years now, but I grew up there. I wouldn't be surprised if your analysis on urban vs. rural centers being producers vs. consumers might be slightly off as the economy is heavily dependent on agriculture etc.
New Zealand has two major problems: 1: Housing is completely out of touch with reality in Auckland (and to a lesser extent in all major centers). Auckland is one of the least affordable cities in the world to live in, and unlike San Francisco, lacks an industry that pays enough to keep up. 2: The regions are suffering from a death by 1000 cuts type scenario.
I have a working theory that the move towards bigger and better and more powerful cities has been one of our gravest errors in modern urban planning.
Regardless of how optimal for the nation that might be, or even if everyone is actually better off, you can easily end up with many unhappy people outside of Auckland (a political problem).
Edit: strongtowns on cost/benefit analysis (half good, half not): https://www.strongtowns.org/journal/2010/12/21/best-of-blog-...
If Alaska consumes a lot of tax units by having an early warning system for ICBMs, then Alaska benefits in the sense that there is a government jobs program, but the simple calculus of tax units consumed vs produced doesn't factor in the benefit San Francisco and Los Angeles get from the early warning system.