Are you planning to visit Devonport?
The Folk club there meets on a Monday night and I reckon that's NZ's best!
Look for Roger Giles - he lives in Cowper St., Devonport and runs the club (or at least, he did the last time we went there).
Even if you're not going to the club, the Devonport ferry ride and walk up Mount Victoria is worth the effort - the view is lovely.
Cheers,
Robyn