Not really. Fundamentally, besides the high costs (and therefore critically, reduced quantity), the issue is the balance between military and civil missions. The P-8 is not really a great airframe for finding lost yachties and fishermen in the vast South Pacific (where you may need to fly low frequently). The USN P-8s didn't even have an air-droppable liferaft package fitted iirc. The question that needs to be asked is: is the primary mission of the aircraft as a coalition asset that can seamlessly slot into out-of-area missions (such as the P-3K2s have recently been doing in the Arabian Gulf), or is the primary mission patrolling the South Pacific for said lost yachties/fishermen and illegal fishing vessels? My money is on the latter. The South Pacific is hardly an ELINT hot-bed either. To my mind the P-8 gets the balance quite wrong for NZ's roles. The P-1 on the other hand, would excel at the SAR stuff, while still being fighty / sneaky enough to do the out-of-area jobs well enough (in the Gulf we were looking for Somali pirates, not Soviet battlefleets)
I have several issues with the above, some due to a difference in opinion, others due more to a different appreciation for certain capabilities from a SAR perspective.
The first has to do with the balance between civil and naval/military missions. Whilst I absolutely agree that a fairly significant segment of the NZ population and gov't/political body sees the civil missions as of the greatest importance, that directly relates to why a number of DT posters have been banging on about for years, this "sea-blindness" that is so surprisingly common for Kiwis to have, given that NZ is a remote island nation that is active in international trade. NZ has SLOC's between it, and every international trading partner NZ has with ports. As has been demonstrated, conditions along those SLOC's can and will impact NZ. IIRC when piracy off the coast of Somalia had gotten particularly bad, it caused the average commercial shipping insurance costs passing through that region to rise ~USD$100k per voyage. Depending on what (if any) measures a shipping company took to decrease the threat/risk, there could have been additional costs due to increased fuel consumption due to route/speed, the cost of an embarked security team, etc. One must also remember that this was just caused by pirates armed with small arms. Imagine the potential havoc and resulting increased costs on international trade and trade to NZ that a rogue sub or mine-laying vessel could cause, operating in one of the SLOC chokepoints, or even worse, if hostilities were to break out and a nation's subs and naval vessels to do close a SLOC.
If the NZDF is not properly kitted out, then if (when) such a scenario arises, the NZ gov't of the day will have no way of providing or contributing a response to such a sequence of events. NZ assets might lack the persistence required to cover areas desired, either as a direct response to the threat to the SLOC, or as a replacement to cover a friendly/allied area as they shift assets to respond to the SLOC threat. It is also possible that NZ assets could be below a certain level of capability deemed relevant or useful, which could easily be the case if the sensor range or resolution is too low, or if the datalinks and comms freq/bandwidths are not what is required.
Broadly speaking, NZ can opt for either 1st tier, 2nd tier, or 3rd tier maritime patrol aircraft, or a mix of the above. I freely admit that I do not know for sure, but I strongly suspect that both the cost and capabilities for the 1st tier options are going to be more or less comparable, with the P-8 IMO likely having the greater current and future capabilities overall. The Kawaskai P-1 is another option which I consider comparable to the P-8. At present, I would not really consider a Saab Global 6000/Swordfish due to some of the recent articles and claims which have been made about it, given that a number of them have been factually inaccurate or exaggerated. Further, some of the claims which cannot be proven either right or wrong (due to a lack of data) are logically flawed, in much the same way that early claims about the Gripen NG were when it first started getting developed. One cannot get bleeding-edge capability without the costs and risks associated with developing bleeding-edge tech, and using MOTS tech and the associated greater likelihood of reduced developmental and integration costs will not provide bleeding-edge capability.
If costs and civil missions are major driving factors, then just getting 2nd tier capabilities might be sufficient to meet some of the civil and naval/military needs of NZ. IMO however, this reduction in both raw and relative capability for the NZDF will lead to NZ being excluded when events and decisions occur that are of interest to or impact NZ.
With respect to the importance of low altitude operations... that is assuming a few things which seem to be incorrect. One of the first is that apparently one of the intentions of the P-8 Poseidon design was to equal or exceed the aircraft performance of the P-3 Orion in terms of loiter at range/altitude. From a cached RAAF document, the P-8 Poseidon can travel 1,200 n miles, then loiter at low altitude for 4+ hours, which is the same distance and low altitude loiter time for the P-3 Orion. One of the primary differences between the two is that the Poseidon can cover the 1,200 n miles to get on station much faster than an Orion could, resulting in fewer aircraft overall being required to provide a persistent presence at a distant station, as less aircraft and time are tied up in transit. It also makes assumptions about the capabilities of new sensors operating at higher altitudes vs. older sensors at lower altitudes. The higher the altitude, the broader the radar and visual horizons and if working with sensors of comparable sensitivity at low and high altitudes, a the higher altitude flight will be able to search a larger volume in a given period of time. The potential to add in the ability to deploy and control a drone swarm which can provide a linked low altitude search capability would just add to the existing P-8 sensor capability. That might not be of interest for civil aeronautical SAR missions depending on how important civil authorities felt the search was and if the cost was justified, but could certainly be important for military/naval operations.