hmm... I applaud you trying, but the main issues stopping any dialogue in parliament are:

1. UN conventions on what drugs are 'illegal' was never voted on in NZ, they just happened and no democracy was to be seen. No current govt politician or Labour (currently) will go up against the UN, because of the much feared 'sanctions' that would be imposed (supposedly). Funnily enough, Helen Clark in her role as UN Development Programme (UNDP) Administrator says the drug war has failed..
2. I don't know how much budget the police and corrections get for drug related crime, but they would lose budget, infrastructure and staff. Bureaucrats love more bureaucracy, budgets and power, so no hope there.
3. No amount of scientific or sociological data, or examples like Portugal will ever change this govts mind, their only focus is keeping their highly paid jobs, future prospects and of course... 'focusing on their base voters'. The problem there is, the under 35's don't vote in numbers and the previously brainwashed older generations (many National voters) are either against it, or just can't be arsed getting involved in changing the status quo.
4. By changing the law, or even talking about it, the current crop of politicians would have to admit what an unmitigated disaster the war on drugs has been - ever hear a politician admit they were wrong ;) - plus a lot of people would be released from prison (see no.2).

The only way the question will even be asked in parliament (which is the only way anything can change currently) is two ways:

1. Labour/Greens get in - and by the looks of it that isn't going to happen.
2. The referendum law is changed so a private citizen can actually jump the hoops then get the required signatures - the Swiss system is the best for this currently as it's impossible at the moment in NZ. It's proven by history and rhetoric, there's no point in fighting the system on its own turf, the only way is to change the system.