Pacific Premium economy is never twice as much as for standard Y. On a roundtrip from LAX-AKL sometimes it's only 400 more and I think it just may be worth it. Also, although there is no official way to use miles Air NZ's Y+, I remember last year when redeeming LAX-PPT-AKL-LAX, with AKL-LAX being the only segment with Y+ available since the other two are 767's, after ticketing the awards with my DM miles for Mom and Dad, I called NZ to get the booking references(record locators) I inquired about Y+ and she told me she calculated a fee of $200 USD per person to move up from Y to Y+.