Several interesting insights in your post Ian,
...we've lost so much in the process.
I've personally come to see American evangelicalism in three phases since the Methodist societies first came ashore in the mid 1700's.*
1) First hundred years- Communities and societies of God. (Exemplified by John Wesley)
2) Second hundred and fifty years- Salvation machines. (Exemplified by Charles Finney)
3) Currently--A free market for domesticated private religon (Exemplified by Bill Hybels)
It can be fairly said that regardless of the particular driving forces, that the idealogy of the market has triumped in the American church, even among the most committed bible believing Christians. (edit: vs. the idealogy of family or community) As an example I was talking to a brother last week who declared in a matter of fact manner, "I'm only here untill the Spirit calls me elsewhere. I follow the Spirit."
Whether 'lured away' by the world, or 'called to' another church, the bottom line is that American Christians are generally divested from one another socially. I do not think this is simply a defect in American character, but an effect resulting from the emergence of the more personal economic vision of the American information economy. In the 18 and 19th century the American dream was land ownership, and the 20th century the dream was lifetime employment and pension; both of these personal dreams were also coorporate as they required a more stable investment and interest in community.
In our current information age, the American vision of financial security is almost completely personal and portable. In the past my security was in the well-being of my village, and church community because my well-being was inseperable to the well being of my land and my house. Nowadays, being mobile and detached is a vital and distinct economic advantage.
I believe this is an overlooked (edit: non-spiritual)factor in both the decline of traditional denominations (which were originally built upon long term family relationships that afforded stable commitment to a community or organization's beliefs), and at the same time the growth of more charismatic and seeker sensitive denominations (edit: which are better able to offer satisfying "religous feelings" while requiring almost no lasting commitment to the organization or community beliefs). To quote Thomas Dolby "I live in a suitcase."
I'm not commenting here how one segment is better then the other, only offering some observations on differences that I've noticed between the two. In fact, the social-economic reasons outlined here are nothing that can be held against any denomination of the American Church for it's decline, anymore then we can blame an declining species of wildlife for the encroaching suburbs that reduced it's once healthy environment. In other words, this is not yet another reason to be mad at the church...but to perhaps have mercy for the sincere Christian who feels alone and isolated.
MC
(*edit; see "The Way of the Cross Leads Home" by A. Gregory Schnieder)