In my opinion, if NZDF requires an aerial fire support capability beyond the increased capability it is acquiring through the SH-2G(i) SeaSprites, the easiest and most cost effective approach, would be to acquire a precision air to ground weapons capability (in addition to their extant anti-ship capability) for those SeaSprites and for the AW109 LUH fleet to cover littoral and overland missions.
An expanded AW109 LUH fleet would be easily and quickly obtained, straightforward to introduce into service for the RNZAF and would be cost effective. Armed AW109's would have little in the way of developmental risk, given weaponised AW109's are quite common in airforces around the world, as the attached photos indicate and as specified by the manufacturer with various armament and equipment options available:
AW109 LUH | AgustaWestland
Australia used to maintain an "operational" capability for armed helicopter operations based on 6 UH-1H Bushranger helicopters, so an "operational" fleet of 6 or so armed AW109's could provide a genuine operational capability for precision aerial fire support for your land forces. Deployed as a two-ship mini-flight, such a capability would greatly enhance the combat capability of any deployed NZ force.
For the higher end warfare roles, an anti-ship missile / stand-off land attack capability for your P-3K Orions (and possibly the ANZAC Class frigates) would provide a potent capability to secure your maritime routes and contribute in a greater manner to regional security operations in the Asia-Pacific region and combined with the SeaSprite / Penguin ASM combo would offer significant flexibility and attack options for any Asia Pacific conflict scenario you might like to consider.
For the same price as a flight of new-build AH-1Z Cobras, you could acquire much of the above capability for NZDF and I think the all-round capability benefit doesn't lie with the Cobras...