I am definitely a supporter of STV in NZ, but it won't happen. There are 8 unions and 2 political parties in support of MMP and only one small organisation which opposes it and this movement hasn't adopted an alternative.
The main reason we will see no change however is that John Key says he likes MMP -the people love Key too much to disagree with him.
I also agree that NZ should be a republic, and our flag should be the silver fern. If this does happen it will happen after Queen Elizabeth is no longer Queen.
Oh yeah, I've no hope in hell STV will get up in the referendum, though I'm certainly going to do my best to advocate it to anybody who will listen (i.e. about two people, and a few walls).
Totally with you on the flag thing.
I've no comprehension of New Zealand's attachment to the Queen or the popularity of that bland schoolboy John Key, but I suppose those are getting beyond the scope of structural changes in this thread and much more onto contemporary politics ...
I am however, against compulsory voting. Firstly, if you need voting to be compulsory for some people to vote - I fear for who those people might vote for! Secondly, forcing people to vote against their will forces them to condone and endorse a certain politician or party - and I don't think you should vote if you don't think what a party or candidate does is OK with you
I'm not particularly hung up either way on whether the vote should be compulsory or voluntary, but as somebody who is active in both Australian and New Zealand politics, I feel like it works well in Australia. Primarily, it reduces all the cost and fuss associated with "getting out the vote" and compelling people to care enough to show up in the first place. Parties and campaigners can get on with campaigning rather than having to pause and encourage people to vote all the time. New Zealand is lucky that we traditionally record high voluntary turn-outs, but we need only look to the US to see how bad it can be.
Moreover, I would consider voting a civic duty akin to paying tax, and voting requires far less effort to do. It reduces problems associated with access to the vote, and quite importantly means people show up even when the weather is bad (seriously, compare the turn-out at any Kiwi election on a nice day to any election on a miserable one; it's lower at the latter). And, of course, if somebody really doesn't want to vote, nobody is stopping them from getting their name ticked off the roll, getting their ballot, intentionally spoiling it while in the polling booth, and dropping it in the ballot box. Just look at the high number of protest informal votes at last year's Aussie federal election.
There are abstract arguments that compulsory voting generates greater political awareness (people have to vote, so they are more likely to take time out and learn something,
anything) and gives the victor more legitimacy. I'm not sure if any major studies have been done for or against those propositions though.
But I'm certainly sympathetic to some of the arguments against - as you say, god knows who some non-voters may vote for out of sheer ignorance or apathy (I like to play a game at election time to see what totally unknown people with "cool" names poll better than equally unknown people with commonplace names), that there should be a freedom to chooe not to vote if unsatisfied with any of the options, and that compulsory voting potentially benefits large parties to the detriment of smaller ones as uninformed voters vote on the basis of name recognition. But given the arguments in favour of compulsory voting, and the fact third parties are very much alive and well in Australia, I nonetheless incline towards it. Though it's probably not an urgency at the present in New Zealand - maybe if turn-out nosedives, it's worth more consideration.
Phew! Did I really write that much on something I tacked on as an afterthought? Forgive me.
Though I've spent a decent amount of time in Wellington and Nelson the last few years as well as on the North Shore. I tried to get some time on the Kapiti Coast last year but only managed a couple of days. 
Oh, that sounds like an interesting story, I did not know NZ was unicameral. In the states we only have, weirdly, Nebraska that decided to do the unicameral thing. I too was half-drunk while starting this post so that's why #1 in the OP is written a little loosely. 
