Ooh you're all very helpful as usual, thank you. I think it would be great to be able to continue to do interesting voluntary work in NZ - this is all assuming INZ approve us which is going to be a long way off since we don't submit our ITA until tomorrow - just got to collect the blood test results then it's off to the Post Office, clutch of lovingly prepared and carefully ordered paperwork in hand!
I think some of my original confusion arose from a JP friend here who hails originally from NZ - her situation was basically the reverse of mine a couple of decades ago, and things are bound to have changed in that time.
Many thanks again.