Judging by some of the video/photos there could be an increase in used car sales between now and end February, especially in Auckland, as folk replace flood damaged write offs. Most people who had a vehicle in that circumstance will feel they need to continue to own one, and any insurance payout will be reinvested in a replacement fairly promptly.
But Auckland private market buyers in particular will need to be vigilant for a year or two to be sure they are not getting a lemon resulting from this event.