Forget about this idea. Apart from all other issues (availability, B/Y ticket...) you most likely did not consider that upgrades are done based on segments. That means 2 pax Europe-SIN/BKK/HKG...-AKL will need a B/Y fare AND 320k M&M miles together. Only exception might be the mentioned direct NZ flight but still it stops in HKG/LAX so I'm not sure about the segment rule then. Just to compare: 2 award tickets in C to AKL with M&M are 370k (plus fees and taxes).