Given that it's over the holidays and there will be high loads between NZ and the motherland, I think your chances on the return leg would be pretty slim if you wait until the outbound leg to lodge upgrades for the return. Especially since you're returning through LAX where you have scads of cashed-up Americans coming to holiday in NZ.
If you want to maximize upgrade chances, lodge EAPD upgrades now.
If you want to maximize the chances that you're sitting up front, book BP and be done with it
