For another reason why fitting the P3Cs with Harpoon may not have been pursued, take a look at this recent press release from the US govt on their recent Harpoon sale to Brazil.
http://www.dsca.mil/sites/default/files/mas/brazil_14-09.pdf
The money quote is
That's $169 mil USD for 16 missiles, plus training and all the add-ons. As near as dammit $200 mil kiwi.
Hell, we could buy the littoral warfare support ship for that, or 3/4 of a tanker. Either of which would get a lot more use.
If these costs are in any way comparable to what NZ would face, I'd say we have better ways to spend the money.
Keeping in mind that the deal includes training, parts/spares, and "related" logistical support. Going off pricing mentioned at
Naval-technology the per-missile price for an AGM-84L Harpoon Block II is between USD$1.6 mil - 2.0 mil. and that is based off fixed price contracts with Boeing in 2012 and 2011 respectively. This would be that the cost for just the missiles for Brazil would be ~USD$32 mil. or only about 19% of the total contract cost. That leads me to believe that the support package being purchased either covers significantly more than the article appears to suggest, or that the training and support will be for more than just 16 missiles.
I don't know enough about the ins and outs of what was proposed to understand fully what happened, but I think it would be worthwhile reflecting on a couple of possibilities.
One possible reason is ideological. It's entirely possible that the government of the day didn't see an armed role for aircraft. However, I doubt this in itself would see a political intervention dictating how the wings were wired (it's unlikely to have been a distinctly identifiable part of the aircraft rewiring).
It would be hard to rule out timing either. On a project risk management basis, introducing a new capability and the subsequent integration issues into the mission systems may have been seen as an avoidable risk in a project that was primarily based on restoring and enhancing a C3I platform.
Policy and doctrine seem the most likely reason to me. A response that would require a long range anti-ship missile is only conceivable in the output classes relating to major changes in regional security, where the territorial integrity of Australia or other aligned states is directly challenged, or where trade routes are threatened. In those scenarios its inconceivable that you'd be using a P-3 in a maritime strike role by itself, purely for doctrine reasons. Western doctrine typically calls for coordinated missile strikes from multiple axis arriving on target simultaneously. That simply can't be achieved by one P-3 - it's the wrong tool for the job, and is too expensive with too many crew to risk.
On the other hand, if you're Brazil and your planning included the possibility of your maritime patrol platform having a chance encounter with a hostile neighbor's submarine on the surface, you'd be silly not to have capability to take the shot at it - it might be the only chance you get. If the RNZAF was still seriously in the business of hunting submarines it might be a useful capability, but it's not.
A few things about this, that people seem to either not be understanding, or missing. The wings themselves AFAIK were/are fitted with MIL-STD-1553 wiring, before and after the re-winging. What was not done during the re-winging was to upgrade the wiring to the MIL-STD-1760 electrical interface. What this means in terms of service capability is that the P-3K2 can carry/drop/launch external stores like Harpoon (Block I), Mk 82, etc. Where the lack of a MIL-STD-1760 interface gets felt is the ability to use the more advanced munition capabilities, targeting pods, etc. A P-3K2 hypothetically could carry and launch a Harpoon Block II at a target, but detection, targeting and guidance would rest solely with sensors and computers onboard the Harpoon itself. The much more capable sensors and computers aboard the Orion would have no communication or control over the Harpoon, because the interface between aircraft and missile Is incompatible, preventing the aircraft avionics from 'talking' to the Harpoon.
As for the notion that not including an interface upgrade was to reduce programme risk over adding new capabilities... I personally doubt that for a number of reasons. For one thing, the change itself has to do with the wiring interface, and the change would be to a newer standard for the connections, not something particularly costly, difficult, or risky. The other is that by changing to the new interface, it did not add new capability to the P-3K2 on its own, but it would allow the Kiwi Orions more flexibility in the future for capabilities.
The new (like around and in service for a decade or so now) external stores like JDAM's, PGM's, fuel drop tanks, targeting pods, etc all use the -1760 interface.
By not having those interfaces changed, the ability for the P-3K2 to keep up with new developments is made more difficult and costly. Granted they could still get the interfaces updated, but it would require removing the wings and opening them and parts of the airframe up.
In many respects I equate the refusal or failure to upgrade the interfaces to being the same as a homeowner who does a full scale renovation and remodel of their home. Complete to the point that their home was stripped down to the studs and framing, but the homeowner refuses to have the electrical service in a significant portion of their home upgraded to current standards, instead keeping the 1970's era wiring, ungrounded sockets, fuses instead of circuit breakers, no GFCI's, etc.
Given that the risky and expensive part (re-winging) was already being done, a failure to keep potential future options open by updating the interfaces at the same time seems almost to be a deliberate action to limit future capabilities.
-Cheers