In my view it's essentially a Ponzi scheme. More and more people coming in drives house equity "growth" and increases tax take with a lag on the demand for corresponding tax expenditure.
Unsustainable in the long term of course but the last 3 govts haven't let that worry them.
Of all the weird and wacky data points illustrating our peculiar economy, perhaps the most overlooked is the number of people still arriving in and departing from New Zealand.
Overlooked by the media I suppose, probably because they have been cowed into thinking that bringing it up means you're some kind of xenophobe or racist.