I fully agree with you guys that this track is totally useless. It was extreamly expensive and a waste of tax money IMHO.
Back in 2004 I visited the construction site and by that time I thought that they'll finish it rather soon. Unbelievable that it took them another 5 years to get things done.
BTW: If you don't have any luggage the Brandenburger Tor is within walking distance to the Bundestag and Hauptbahnhof anyway.