Maybe the best thing is to be radical.
We know what the earlier people did, its in the record books. If you have extracted everything out of something, whats the use of storing it now?
So move the old structure to a new place, reconfiscate the land and start some new good construction there. Usually the land in such cases has become very costly.
The best solution is to use it in best fasion. But this should be done only when you know everything about the structure and about the people associated with it and when the demolishment does not hurt the publics sympathy to the structure.
Who knows, while breaking the structures, you find something new?