Peak season down under (Oz and NZ) is Dec to mid Feb. I'm guessing but Mar may still be peak (as far as airfares go) or may be shoulder. Wont be low season.

Key dates in NZ lists public and school holidays, when things can be busy (flights, accom, road traffic). Australian public and school holidays are very similar. Early-mid Mar 05 misses them all.

There are specials LAX/SFO-NZ or Oz on Air NZ, Qantas and United from time to time - can be quite a lot cheaper than the figures you mention, but not sure how much addon from PHL (of course you could buy that separately). Check out NZ and QF fora as these specials are usually posted here. Of course the specials do have restrictions so may not suit your needs.