I don't think the Air New Zealand crew got anywhere near 500' AGL. They realised quite early on that the GS was wrong.
"Approximately 6 miles from the runway threshold a missed approach was carried out from an altitude of about 400 feet."
from here:
http://www.icao.int/icao/en/ro/apac/cnsmet_sg6/wp39.pdf
To all, out of interest, does your company have a SOP glideslope check that uses the DME at say 10DME (or the distance when the ILS starts) as opposed to the Outer Marker?