Berchtesgaden and Dachau are awkward to see by public transportation, but not so for Salzburg. If you think you'll be in Munich some other time without a car, I would focus on smaller towns without good train service.

Part of the castle road (less known than the romantic road, but they intersect in Rotemberg--spelling?) isn't far from Munich. Germany also has a bunch of nice wine roads in different regions, although I can't think of any that go close to Munich.