As a financial member of a club (assuming there is one in your area) or you can become a distance member, you receive the club newsletter via email. You also, in belonging to a club, belong to the FNZAS and receive the aquarium world magazine 3 monthly. Its produced here, in NZ, so pretty much everything in it is relevant to NZ fish keeping. There are also small discounts available at some of the pet shops for FNZAS members on production of your membership card as long as you ask politely. Membership is not expensive.
So, you get to meet other like minded people, share ideas, go to events like tank crawls, quizz nights etc, get a chance to swap things like plants, fish, at the local club meetings (this sure beats having to pay out every time you want something especially when you have a cupboard full of unused stuff). You also get to have a say in whats happening in the federation at a local level. Each club has delegates to the national body. If you want you can go to the conference held around NZ each year (this year its in June in Tauranga).
To me its been invaluable. I now know a lot of good people with incredible knowledge. I have had the chance to visit members in other areas and have a look at their tanks, talk to them and swap ideas.