That is the argument that Angry Bear is considering (although he hasn't formally argued for the connection yet). I think this question he poses is interesting:
But this leads naturally to an interesting question: Does liberalism cause higher income? Or does high income cause people to be more liberal? Or is there some third variable–education is a natural candidate–that causes both higher income and more liberal attitudes?
I think to an extent liberalism can lead to wealth. Obviously a public education system, child labor laws, worker's unions etc. laid a good foundation on which to build modern American capitalism. But, I think that can be taken too far, like modern day Europe where high tax rates to fund vast social safety nets can stifle growth.
I do think the reverse is true, that wealth causes liberalism. Developing countries don't care about the environment, because the people there are more worried about making ends meet day to day. And many of these "sweatshops" that are despised by American liberals are actually the best jobs in those countries. Hell, 100 years ago factories here in the United States were in a similar situation. It is a stage of development.
I guess the argument depends in part on how you define liberalism. Modern day liberalism will stifle America, in my opinion. It seems to be a "we know what is better for you so we won't let you make your own decisions" ideology. But liberalism of 50 or 100 years ago was different, and I confess I don't know much about it (despite my love of nonfiction books, I don't read much history). So, keep an eye out for Angry Bear's next argument. It could lead to some very interesting discussions.