Simple living came upon me when I started asking myself to draw the line that divides the NEED and DESIRE. It's a fine line that helps one to stay focussed on the Life's moment. That's a personal change.
On the social front, a change is warranted in multiple dimensions considering the enormity of the problems we face today; perhaps we need a solution that’s too big to be comprehendible by human minds; a change that involves multiple stages of implementation spanning across a few generations/ages. And a change in the course of humanity's evolution towards inward senses is the first stage of the solution and its implementation is already underway. Next stage perhaps is about aligning the consciousness of these simple living individuals to that of the Earth Consciousness (I strongly believe and feel vaguely that EARTH is one living organism)
Another dimension to look at is the DIVERSITY. In Nature, no two things are alike (every life has its own signature) whereas in the man-made world, mass production is the norm (the only difference between the cars from a car factory is the chassis number) and we haven't learnt the algorithm of mass producing things with unique identity yet.
Globalization in the Industrial civilization is our first attempt towards achieving Unity in the Diversity and we need not be ashamed to tell that we have failed this first time. But we have learnt from our mistakes.
In the next wave following the industrial civilization, the individual shall learn to FEEL the individual SELF(I am sure my definition of the DESIRE Vs NEED line is different from that of yours) and those diverse individuals shall slwoly form patterns by uniting together to grow stronger and SURVIVE as a species! And that seems to fit with the Darwinians' reason for evolution :-)
So, my definition of Simple Living is the process of learning the art of 'feeling' rather than 'thinking'