As far as I’m concerned, if it isn’t worth buying without being labeled/marketed as “Christian” (or pagan/Jewish/womyn-made/etc.), it’s not worth buying because of that label. If it sucks, it sucks. If it’s mediocre tripe, it’s going to be mediocre tripe whether it’s “Christian” or not.
I’m aware of exactly one Christian recording artist who has had any success outside that small market — Amy Grant. She’s not setting any sales records as far as I know.
I realize there’s a hell of a lot more to being good than just being marketable and marketed well, but most of the material I’ve ever seen marketed with one of those niche-market labels just isn’t up to par.