This was implemented back in the glorious Helenista days - 2002-03 - as a 'solution' to the relative (even back then) inability of the battlers to get housing finance.
The unintended consequences (which, as most textbook cases do...) only emerged later.
Picking a figure at which to pitch the loan to the aforesaid battlers, took a regional price point. Of some derivation, obviously, but most likely a median/average/PDOOMA of recent sales.
This figure ($100K for Christchurch, around $350K for Awkland IIRC) ignored the fact that property could be had at very substantially less than that figure, particularly for battler purchase - small, run-down, 'needs TLC' etc.
So it served as an instant, universal oopards pricing signal for all sellers simultaneously, at that end of the market. After all, why sell that collapsing shack, for which one had privately estimated that a canny buyer would pay no more than $183K, at less than the Glorious WH loan figure plus a Modest Profit.
Which is exactly what happened. I've related my own case here - nice work if you can get it.
If we estimate the extent to which this new pricing floor conferred instant CG to tens of thousands of low-end houses, we could say an average increment of $100K, times say 30K homes in Awkland - that's $3 billion CG.
Now divide that CG thus conferred, by the number of WH loans ever advanced: say 10K.
It works out to $300K advanced via CG per WH loan.
It also explains the precipitate jump in the rate of increase in house prices thereafter, at least to some degree. Because the reaction to the re-pricing across the board was, oddly enough - 'hey, we cannot find a house for the current WH loan limit - better raise it'. E.g. here:
First home buyers can now borrow up to $350,000, up from the previous cap of $280,000.
Which, unsurprisingly - set off another round of universal price increases....which set off another WH loan limit increase which.....
The Welcome Home Loan was introduced in 2003. Between its inception and May 2009 a total of 4,482 Welcome Home Loans have been settled, translating into access to home finance of over $719 million.
The above works out to $160,420 advanced per loan. Compare this with my (quite possibly chimerical) figure of $300K given away in unearned CG via Universal Higher Price Floor, to all and sundry....
And even today, who, in their right Economic mind, would sell a house for less than the current WH loan limit? Because the essential qualification - 'can you fog a mirror' - is fairly straightforward.......
My contention is that this was easily the dopiest, most economically damaging policy, invented in recent times. Markets for houses are slick on the upside, sticky on the downside. They certainly don't need stoopid Gubmints incentivising mass upwards re-pricing....but that's exactly what happened.