LudditeJourno has an excellent piece on the difference the Maori seats have made to indigenous representation in New Zealand. The whole post can be summed up in this one graph:
(Note that New Zealand's Parliament is much smaller than any of the others)
The Maori seats have ensured that Maori have had representation - unlike the indigenous people of Australia, the US or Canada. They have ensured Maori have had a voice. It may not have been much of a voice, and it may have been ignored for much of our history (the way Parliament behaved towards Maori MPs in the C19th was simply appalling), but its been there, and its been worth something. It's made our Parliament far more representative than it would have been, and been a perpetual and powerful reminder that we share this country - something people like John Key seem to want to ignore.