Depends on age and stage.
Personally I think it is pretty hard to justify comprehensive or super-type covers - the ones that pay for routine doctor consultations and prescriptions. Those are pretty expensive and you would have to be having a lot of consultations to make it stack up. And that assumes you are organised enough to keep the receipts to make a claim etc. (I'm not). Though it might make sense in some circumstances, but I'm not sure what those would be.
We do have surgical cover though with a decent excess to balance out the premiums. We're lucky enough to be reasonably fit and healthy and on reasonable incomes. While it would definitely be a grudge purchase, we can pay a $1000 or so medical bill for a scan, diagnostic or very minor medical procedure if push comes to shove. However a $10K or $20K issue would be another story.
Dynamics also change a bit when you have kids. When Littlest Miss MDF was 2, she needed a reasonably urgent but straightforward procedure. Not life threatening or anything but was looking at a 4-6 month wait on the public list but we had it done the next week privately. The peace of mind for that was pretty much worth the price on its own.
I suspect we're behind on the premiums vs claims over the lifetime of the insurance, but that's basically the nature of insurance.
Overall I think NZ's healthcare system is pretty good and will help you with the big issues - save your life heart attacks, cancer etc. But the more routine, not save but improve your (or your kids) quality of life can be a bit more hit and miss. I think it basically comes down to if you had a sudden medical bill for something, how much could you afford out of your own pocket?