I personally only buy them fo my business (which is located in NZ, I'm in NZ) but I don't think they are going to turn out like the .com's where everyone is trying to get LLLL.com
Depends on who you are targetting. People in the UK for eg are used to typing .co.uk when putting in domain names. I usually end up using .com.au (am in Australia) when putting in domain names as well. So, if you are targetting NZ people, having a .co.nz domain would make sense in this respect.
I think it would worth it if you have a unique and brandable domain name that was available in most countries where the domain was not taken. If it was a large venture website establishment.
Unless you live in NZ or planning to start a business there, I wouldn't waste my money on them. Isn't it just NZ & Aussie people the only ones that can purchase those names?
Yes, you can only purchase a .nz or a .com.au if you have an established business and ABN in those countries. It also cost around $70 - 80 per .com.au Domain, so it you were going to invest, if you had a way of purchasing one, I would be hoping for some return or it could be detrimental