A lot of discount economy fares on Air NZ don't credit to other FFP, atleast with Airpoints you get Status Credits too, and remember Status Credit earnings will not be changing (just airpoints themselves). The most useful thing about being NZ*GE (other than *G) is that standby upgrades can be cleared 330 days in advance (R Class U/G Class for GEs).

I feel your pain about the devaluation, especially when Air NZ is expanding its partnerships with useless partners such as Flybuys, but I think its still the best option if you can maintain G/GE.