I am not the great thinker you are (Wind in His Hair to Ten Bears), but IMO the shell of the building represents what is left once the takers in society get done with their taking leaving nothing but a shell of what greatness once was.
The new offices of the John Galt Line, regardless how tattered they may currently be, represent a new hope for a future that can be rebuilt from the bottom up with hard work and determination.
Most of us at FR are great thinkers. (Maybe that should be my next tag line.)