While I agree in the expensive bit you have to admit the F-100 is a general purpose design that happens to excel in air defence. It has a VDS and an ASW Helo in addition to the hull mounted sonar and ASW torpedo tubes, I don't know what else you could do to make it a better ASW platform, VLASROC, a second helo? Don't forget the Harpoon, 62 cal 5"gun and 20mm (F-100) 25mm Typhoon (Hobart) aft of the bridge wings. Its air defence capability doesn't limit its versatility, in increases it. I would suggest that the F-100 exceeds, rather than fails to meet the RNZDF.Think they are pretty munted aren't they, so we'd be swapping one munted lot for another munted lot.
The NZG wouldn't go for the Hobart class destroyers because they wouldn't meet the needs of the NZDF. They are to specialised and expensive. The Spanish F100s are similar as they appear to be primarily designed for air defence. I think that the RNZN is after a more GP frigate that incorporates very good ASW and AsuW suites. Three would be far better than two. But the idea of replacing the two ANZACs early does have merit and a GP version of the F100 would be interesting. It would make sense as it's a relatively new and proven design plus it would tick the box of commonality of with Australia.
It’s more a question of are there platforms that can do what is required for a lower cost; I would hazard the answer is yes. Would the RNZDF like the extra capability, probably; would the government pay for it, probably not.