In terms of aesthetic value, no, the means by which a work is produced is of little relevance. Yes, this means that the music of, say, the Jonas Brothers cannot reasonably be said to be of inferior quality just because it was made for easy consumption by white, middle-class, Christian girls in their teens (i.e., for money.) Other metrics might be used instead, but it's doubtful whether these would not amount merely to elaborate rationalizations of prejudice against "mainstream" anyway.
In terms of political value, however, the category of "mainstream" becomes more important. That's because when something becomes "mainstream" it means that its political message has been absorbed and accounted for (and therefore nullified, "neutered," or disarmed) by the system it was intended to disrupt. Or if something was never intended to carry a disruptive political message at all (i.e., it was made for and by the "mainstream") then it inevitably reflects and (even if unintended or blindly) affirms the values, good and bad, of the "mainstream." Thus if you believed, for instance, anti-semitism to be bad, and you recognized it as something deeply embedded into the "mainstream" productions of your society, then works produced by the "mainstream," or subversive works reabsorbed by the "mainstream," would be of lesser political value to your goal of eradicating anti-semitism.