I think you've already put your finger on it in your assumption - a bawdy song is a funny song by definition. That's the point. No matter how extreme, if a song is funny it works, if it doesn't at least try then it's prurient without redemption - that's pornography, not bawdry.

But I much disagree in the other issues. No matter how extreme, how strong the language or adult the situations, the song will work if it's funny and just a good song for the usual reasons - tune, narrative value, etc. If a particular audience gets hung up on a strong word or two and loses track of of the text then it was wrong for that particular audience.

I strongly disagree with repeated reliance on substitute words - some songs are famous for it and they are the point of the song. But habitual use of this device turns to snideness - juvenile smuttiness - cheap laughs. The laugh is a forced one and, itself, detracts from the theme or story of the song. You might as well Bowdlerize (or Brandize) the songs in the first place.

I think if the audience is adult and you have the courage to present the song as a legit piece of art or story or humor then there are a huge number (maybe 15% of all songs) of bawdy songs well worth singing. As to "shock shlock," I'm not sure how you mean it in this context. I'd agree that just "naughty" words stuck arbitrarily in an otherwise non-bawdy song is pointless. But among the unashamed, non-double entendre songs, well, it would just be a shame to PC them down to emasculation.

Well, that's my opinion.