I flew Air NZ from LAX-AKL-MEL a month ago (and IAH-LAX on a seperate reward ticket). We flew regular economy, but the flight was comfortable and the service was good. Like OrlandoFlyer said, you have to call Air NZ reservations to put in your OnePass number, but once it's in, it will immediately open up better seats on the online seat selector. We couldn't get economy plus seats with my *G, but we did find the seats with the most legroom (it shows legroom and recline on each seat on their website).

With *G, you'll get lounge access at LAX, AKL and MEL. The LAX lounge is quite nice and they will escort you down from the lounge directly onto the plane at boarding time, bypassing the need to wait outside the gate. We also got priority check-in (which had no line at all!) and baggage.

Hope that helps!