Let’s face it, feet get a bashing. You will be lugging plenty on your back, and feet in the New Zealand outdoors usually get wet.
Decent boots are high on the necessity list for full tramping enjoyment, or, to put it the other way, the wrong boots can rapidly curtail enthusiasm.
For a quick spin through Abel Tasman, you can get away with almost any footwear.
The rough rocks on the Alpine Route can rip apart a pair of trail runners. A couple of weeks on the West Coast is going to do real damage to any footwear.
Your feet can get well smashed when you have a pack with two weeks’ food and you are wandering up rocky river beds; decent ankle support is a plus. When you add that full pack load to occasional water crossings, not via swingbridge, ie, wet feet, and the potential to be slogging through mud, and/or snow, a robust type of boot is high on the priority list.
These days boot technology is good enough that you shouldn’t get blisters, even if the boots are new, as long as they are correctly fitted and combined with wearing a solid pair of tramping socks.
Hint: invest in a pair of those woollen tramping socks, or two; they don’t need any thin liners, and the fine merino resists matting and getting scratchy.
Tread: perhaps surprisingly, a fairly softish sole helps with grip on the web of roots you encounter in many of the South Island forests.
Long gaiters are highly recommended: they help keep water/stray detritus out of your boots, but mostly that mud. And speargrass.
Look after those feet, and you will have one less thing to complain about.