I haven't had the OP's experience my last couple of flights LCY-TXL. Even with a checked bag, I was out on the curb 15 minutes after they cracked the door. The X9 bus to Zoo takes about 20 minutes, and from there you can go just about anywhere on the U- or S-Bahn. The TXL lounge can be cramped, but I'm never there for very long.

I never flew to Berlin while the Wall was up, the train was dramatic enough. Multiple passport checks, the elderly gentleman in my compartment nearly collapsing with fright at the East German border (it was his first trip back to Berlin since getting out of the East in the 1960's), and that weird whitewashed (the platform, the walls, everything) station just outside Potsdam where the East German border guards made a final check of the train before it went into West Berlin.