I think we should look at Micropolitan areas -- cities of 10,000 to 49,999 souls -- as likely areas for encouraging new congregation growth. The United States has 538 such locations and glancing through the list I could easily pick out several that had no Unitarian Universalist congregation -- some had none within quite a distance -- even though they are often regionally important and could support a small congregation, even allowing our low-ball "one UU in a thousand" demographics.
Here's a sortable list of micropolitan areas. (Some areas have more than 50,000 people; its core city is between 10,000 and 49,999.) See any you know? Is there a Unitarian Universalist congregation there?
If James Howard Kuntsler and company are correct -- and I suspect they bear some truth -- the population will have to disperse and reconcentrate in smaller cities to enjoy a decent quality of life. The big cities can only support so many people in a costly-energy future and suburbs -- where Unitarian Universalists largely have established churches in the last two generations -- will decline further.
But even if some Great Energy Miracle happens, can we afford to not be well distributed? Are some cities, at 20, 30, 40 thousand people unimportant? And if there really is a saving Unitarian Universalist gospel apart from liberal culture and esthetics, oughtn't it be cultivated where it would be the most singular?