Updating this thread to note that, although it's not noted on NZ's international lounge directory, NZ passengers in BP can now access the new United Polaris lounge at IAH (note: not open to *G/Koru in PE or Y). It's a HUGE step up from regular UA lounges, with excellent food and beverage options. Gets pretty positive reviews, eg:
https://onemileatatime.com/united-po...ouston-review/
https://liveandletsfly.boardingarea....ouston-review/
For people with access, there's also an Amex Centurion lounge these days which also looks pretty nice. Definite improvement in lounge options at IAH compared to when the IAH-AKL route began!