I've been playing the Berlin wall for 3 years before John Cox's EXCELLENT book was published on it.
You have already found one of my favorite berlin players
Leonid Kritz and Zoltan Almasi are regular practitioners outside of the usual top 10 suspects (Kramnik, Aronian etc).
Another great resource is Kramnik's dvd my path to the top where he talks a little about his berlin prep for Kasparov in 2000.
Another introductory just fun vid to the berlin is FM Dennis Monokrouss part 1+2 chessvideo.tv on the Berlin Wall.
In general, when I play the berlin i'm thinking in general ideas for my plans instead of forced moves. As white and black (since I play it from both colors), I have objectives. As black, I want to trade a set of minor pieces (mostly one set of knights), retain if possible the bishop pair (especially the unopposed light square pieces), and try to create light square targets.
As white, I want to get in e6 with whatever possible, especially with e5 f4 g4 h3 setups on the kingside. If white doesn't hammer home his pawn majority... he might find himself quickly worse or lost.
These types of ideas.