Hmmmm, interesting!
I do not buy the idea of demolishing building as it has negative effect attached to it. Imagine the money spent in building that structure and then it is destroyed in a day. If the building is still much strong, I think restructuring of it inner and outer structure should be the best option to take.
Although there are exception to the above. And that exception has to do building structure that a dilapidated and beyond repair. Like you have said, building from the 60s and 70s, that is a long way back, and such building need to be built all over again.
If not destroyed and build over again, it might not last and it will be exposed to other havoc when the building is use for any activities.