Seems a lot of kiwis have trouble driving sensibly on the left hand side of the road at the moment - hate to think how changing it would work out! The death toll around a change-over would be significant.
Can't see any benefit from what would be a massive expense and logistical effort.
Would be much cheaper (for random example and keeping on the traffic theme) to give everyone in NZ a new fully electric car and build a full charging network. At least once that was done the country would save huge amounts of foreign exchange each year from reduced oil imports.
Given that the government has been less than luke-warm on encouraging EV uptake - presumably because they dont want to spend anything on it - I cant see them being convinced that changing the side of the road that we drive on would be a good investment.