Air NZ changed planes on us - no more Economy Stretch?

We're new to Air NZ. We're booked on a flight SFO-AKL early Oct, and we each paid $175 for 'Economy stretch' seats. Booked months ago. Today we got an email "Due to a change in aircraft for your upcoming flight on NZ7 SFO - AKL, we aren't able to allocate you the seat you selected. ... We have refunded the seat selection charge ..."

So we went online and found ourselves seated near the back. We looked at upgraded seat options, and the only thing available was 'Preferred Seat' for +$60. I assumed this was going to be extra legroom, but further investigation confirms it's just 'closer to the front'.

Interestingly, old plane and new plane are both 787-9. Uncle Google tells me they operate multiple variants of 787-9, with only the 'V4' having the 'stretch' option.

So it looks like I'm stuck on a 14 hour flight (possibly the longest of my life) in a regular economy seat! Ticket is non-refundable so I can't shop around for better options I guess. Way to go, Air NZ! I presume there's not much I can do about it ...