Obviously wouldn't bank on it, but I've also had two flights AKL - SFO on UA 787 with a row of three seats to myself in Economy Plus. Happily made a makeshift bed.

Id say a high proportion of pax departing AKL on that route will be Air NZ bookings, meaning it is less likely they will know about economy plus or that you can upgrade, until on the plane.

Even with UA HVP being put in Economy Plus, there seem to be a large number of seats still available as it doesn't appear to be a popular flight.

Bit of potential consolation prize I guess.