The tea party was and remains a true grass roots movement. From what I can tell, the coffee party is anything but. Mentions of the "Coffee Party" as a "thing" mostly comes from fairly affluent, white, and well-educated people who are also fairly moderate in their tone. The push for a truly leftist popular movement in the US will have to come from the people who are presumed to be the principle beneficiaries of leftist solutions (minorities, the poor, and union members), and, with the exception of minorities, probably more than half of them are by now card-carrying tea partiers or in the religious right (as are more than a few minority people). It will take a sea-change in American attitudes for leftist populism following the European model to work.
Also, it seems to me that Air America and the few leftist talk show people just don't appeal to as many people as many of the rightists. People like Rush Limbaugh achieved their initial success in part because they were funny and witty as well as being offensive (which in itself is often funny). Leftists tend to come off more preachy. At least that's my interpretation...but I stopped listening to or watching talk shows years ago.