1. New Zealand has a different political system (parliamentary), which is more conducive to proportional representation than our two-party political system. Indeed, some state constitutions have essentially made it unconstitutional to circumvent single-winner districts. In addition, it would cause conflicts with how we elect our president. New Zealand doesn't directly vote for its prime minister, but we do in the United States. A system that would lead to several chief executives is not really a good idea.
2. Quality of Life is not always a good indicator of the personal preferences of people. I've gone to Vienna, most of the Canadian cities, Paris, and Brussels. They are all fantastic cities to live in, but they're not really for me. I live in New York City and prefer its multicultural hustle-and-bustle. Vienna is gorgeous and peaceful, but I prefer a more exciting life and fewer stares (I'm Asian). Paris is beautiful and has the multicultural hustle-and-bustle, but I've experienced more crime and racism there than in NYC; plus, there's a language barrier. The Canadian cities are nice and the people are very friendly, but there doesn't seem to be a lot of opportunities for what I would like to do.
3. Americans have an aversion to taxes and government regulation, which is why a public healthcare system for all has never really been popular. You would have to fault the American people for that, not simply the country.
4. We have pensions, and they've been bankrupting our state governments. That's probably a good indicator of how generous our politicians have been when it comes to the elderly. You also forget about stuff like Social Security, the higher wages, and the fact that Americans tend to spend more.
5. Check your source. That's simply a perceived corruption index, which only takes into account public opinion. The anti-government and anti-bailout/business rhetoric contribute to the public perception of corruption in the United States. I admit there's quite a lot of corruption in places like Louisiana, Las Vegas, and Chicago. However, as a whole, the United States is still less corrupt than the vast majority of the world. Even then, most of the corruption manifests from stuff like kickbacks on local contracts and not bribery of public officials like judges or police officers by private citizens.