One understands "waena" gardening when one understands that the skill involved is understanding each plant and cultivating it in a near natural state in a place that it flourishes. Most agriculture techniques or even permaculture techniques attempt to modify the local environment to suit the plant. Of course borders on each of these concepts become vague and blurred but--there is a big difference between walking out on ones property, finding a spot X, knowing that plant Y will grow in plant X, and planting plant Y--rather than attempting to cultivate plant Y on site X and using a cat to hammer the land into condition to do so.
As James Lovelock often points out, one of the things that's difficult about the modern "eco progressive" movement in general is that by and large the majority of its proponents are middle to upper class urbanites. While they may be very educated about ecological issues in a theoretical sense, they are often very disattached from the realities and practical issues of a non-recreational life in harmony with the land. Just a little. One large and very well promoted permaculture project right down town Los Angeles comes to mind--while an amazing example of fine gardening--a farm kid would immediately ask how on earth one pays the mortagage on a square block of prime real estate worth 2000 bucks a square foot with bok choy. He may also ask where in this permaculture project one gets the water--to which the trendily dressed vegan anarchal-feminist will point to the pipe, of course, dummy.
So what's special about waena? Not a great deal. It's another type of subsistance lifestyle(that's what they used to call permaculture before grant money was invented) that many of our ancestors lived. Subsistence lifestyles are by nature "sustainable" or people die. Plenty have died and still do and more will yet. This is one of those realities and practical issues of a non-recreational life in harmony with the land. But, as subsistence goes, waena is a particularly good style of a particularly fine climate, and the crops it relies on are particularly fine and reliable. As well, Hawaii is only a 100 or so years removed from this kind of lifestyle being commonplace, as opposed to perhaps 500 in Europe, so the idea of working within a natural state and the means of doing so aren't so lost or alien. Since any sort of better or survivable future will require a restoration of as much of the natural state as we can--pressing new land into service for agriculture, even permaculture, is simply not a tenable option.