This subject has been covered ad nauseum... Try out the search - there's a lot there.
Unter den Linden has a handful of great museums and some car related things including the VW/Bugatti/Bentley store. This is in the heart of Berlin.
Wolfsburg isn't too far by train either.
You also have the Lausitzring and Sachsenring - you might check to see what races are going on.