It has a 4-5yr expiry for AirNZ. Also that if you have not flown any Star Alliance fares I think AirNZ will bill you $30 or $20 if you opt to have e-statements unless you have a Globalplus creditcard or home loan. They also have a joining fee too.

I just did some research. I am going out of Airpoints and maybe leave my CC to get the odd point with Flybuys (NZ retail program).
I heard the plus is for upgrades.
For me, the plus is you have dollar points so you can use them as cash. Ie., if you had them, you can book a peak Christmas trip to Paris and back Certainty.
Another plus is that if you fly to Asia return 3.5x even grab-a-seat specials status points are counted so you can get silver but not that it offers much. Gold is probably too hard in this way.

The airpoints accured are just too low to get a reward ticket and hence the 4-5yr expiry. Maybe the odd trip domestically or to Oz/NZ.

For rewards I found the *A - Air Canada, SIA, ANA are pretty good, same for Egypt and a few othes like that - 60k miles to get a Asia return flight. Aegean or Asiana is pretty good for status. I find that Air Canads is the best for rewards and status but for status 10k (of the 35k) per year needs to be flown with Air Canada.

For the flight in question. Have you already assigned a freq flyer no. onto it already?? If so I am not sure if you can deregister that no. and throw in a AirNZ freq flyer no. Maybe talk to your travel agent. If you have not, you can send the boarding passes and tickets to AirNZ and they wil credit them to your Airpoints but I "think" you need to be a member before you depart. Maybe you can show your Airpoints card at checkin??