The numbers do the talking

One of the big stories leading up to NZ's 20 September election was the effort to boost voter turnout. So, how well did that work? (I base my figures on percentage of the eligible population, and not percentage of those on the electoral rolls. The latter is more accurate, but not everyone enrols, so the former has greater validity.)
The 2011 turnout was 68.3%, and this time was 71.3%. Not a big increase, but at least it was not the decline that some had feared. Perhaps the weirdness of the campaign period (moments of truth, etc.) brought more out. The famous "missing million" of 2011 is now a "missing 975,000".
But the boost in numbers went largely to National. Conventional wisdom is that higher turnouts favour the left. But not this time.
Looking at raw numbers tells it all. The gains and losses in actual numbers of party votes between 2011 and 2014 goes like this:

National  +72865
Labour  –10403
Green  +9984

Thanks to the Greens, the Labour/Green combo declined by "only" 419 votes. This is a pathetic outcome for the left.
National has won over new voters (especially at the centre) even while in office. Labour has lost supporters in 3 elections in a row. This suggests that Labour needs to do much more than "stem the flow" in order to begin to challenge a National Party that is now looking for four terms in office.
Is any one of the contenders for the job of leader of the Labour Party up to the task?