Well, I know both of them, though not listening to them. Nina Hagen is somehow in the news when she does again controversial things :-) When I think of Marlene Dietrich I don't know why, I think of: Hans Albers and when I think of him I think of Heinz Rühmann (e.g. La Le Lu).
Since I also listen at work much to music, I tend to listen in my free time to music where I do not immediately understand the language.
I guess if you would have the need to learn German, you will succeed there. Normally it is just motivation that lacks.
Ok, have a nice remaining day. See you.