NZ has quite a few JNC's as we imported quite a lot of them. I guess because they are already RHD. If you are wondering about parts, why not do a Trademe search for both and see what comes up? I quite like the old RWD Sigmas, but have no real idea about the old crowns so can't really give any advice there sorry. Toyota does have a good reputation for reliablitly? The cars tend to rust out here before the engines give up..
But as for JNC's in NZ and Which one to go for it really just comes down to what you want:
Stock/Nana v Boy Racer
Coupe v Sedan
Rare v common
Easy to maintain v Mechs only
easy to modify v hard to modify
easy engine switch v hard to engine switch
Cheap v expensive
Honestly the list goes on...
I'd leave it as is, but that's just me (that should be my sig)...