Occasionally ZQN is shut for a few consecutive days, but not often; you don't say when your trip is, but with 2 day buffer in AKL you should be OK. Multi-hour delays seem to be more the norm than the exception in the past, so same-day connections from ZQN have been problematic historically. As you note, there have been some minor airport improvements, but these are mainly tangential to the causes of past delays. Also big difference between airlines at ZQN (Air NZ has a capability edge over Jetstar, for example).