I finished my dives in the cold water (15C) of New Zealand. I did only 2 dives in Kaikoura, 4 dives in Poor Knights islands and 2 dives in the Bay of Islands.
Viz was around 15-20m at best in the Poor Knights, 6-8m in Kaikoura and about the same in the Bay of Islands. It was full of salps all over the place and I have seen a specimen about 8m long. It is supposed to get better by the end of summer, as of now, salps is a bit annoying if not doing macro.
I was able to see critters I have never seen before and diving around kelps rather than coral was hmm... different and interesting. But really I prefer coral. ![]()
If I come back that would be to dive Kaikoura for dusky dolphins and seals (late summer again is preferred)
As for the Rainbow Warrior that our kiwi friends rate as one of the top 10 wreck, IMHO you can safely give it a miss. It is only interesting for the historical value alone (well if you are french of frog hater that is). Here is a picture (no flash activated, too much particules and salps for that):

Pictures can be seen on my weblog.