I am with you all the way apart from the very last bit.
Folk music when it is really good leans really heavily on that "write what you know" thing and that it should communicate in a voice understandable to the audience and that the material should be able to pass easily hand to hand / mouth to mouth / ear to ear like oral Samizdat.
So you can't be Folk and avant garde at the same time. You can't aim to appeal purely to bourgeois taste and still be Folk either.
So on AC/DC we agree. Defintely. But for me Nick Cave is a bit too concerned with being literature and a cultural figure to be Folk per se.