The point is Air NZ didn't combine their First class product with anything --- they eliminated it.

Even if Air NZ were to pay for their business class pax to use First Class lounges (and they won't), there's no way most First Class lounges could handle a NZ 747 load of biz class pax. It's simply not going to happen. Also, remember this is an airline that's currently cutting costs to the point of eliminating the kits from amentity kits, serving ridiculously small portions of food, shaving costs on wine, etc, etc for their business class product.