spookily similar (for the SWP and SAm) sections to a trip we are looking at starting in July, but in reverse

All looks fine to me - which FFP are you going to use to get the single award ticket on ANZ ?? Currently it looks like we are going to use UA miles for a *A award - it would be a return, and we'd just throw away the return portion. However, if you are also thinking of doing this, note that *A awards from Oceania zone (inc PPT) to NZ *or Oz are only 20k, so you could fly SYD-AKL-PPT on this award with a stopover in AKL and save yourself the cost of the extra SWP segment.

Hope that helps
Stew