I am a simple liver and in addition to my main book on the subject, I have written quite a bit over 35 years. But I don't proselytize.
I occasionally get questioned about my patriotism and loyalty to commerce as a simple liver. The logic behind the question is that commerce is driven by consumerism. Not really true.
Commerce did not originate with consumerism, it originated from the realm of necessity. Industrial commerce grew strong and vital based on providing for necessity.
Nevertheless, commerce in most of the world long ago out-supplied the realm of necessity and entered the realm of consumerism...satisfying whims and personal goals.
Commerce is currently driven by a large component of consumerism because satisfying customers is the driving force of commerce. Buying products to enhance personal goals is consumerism.
In my opinion, the nature of simple living is also the satisfaction of personal goals, it just requires much less in the way of physical objects. Simple living is more focused on livelihood, friendship and individual authenticity. Those elements can drive commerce just as well as physical objects.
The effect on GNP growth is not obvious. If a median income simple liver takes four friends to a wonderful restaurant and hires a string quartet after dinner around a fireplace and conversation, the GNP effect is the same as buying and installing a hot tub.
Simple living is just as relevant to driving commerce as consumerism. Probably more so in the future.