I have been wondering what would be more practical in a post apocalyptic setting, trying to restore the ruins of old (like refurbishing what can be restored and rebuilding over what cannot be and making the ruined cities livable again by degrees) or tear everything down, essentially turning the ruins into mines, recycle the materials and build anew in other locations?
For additional information the civilization that would be doing the rebuilding would have a level of technology comparable with mid 21st century humanity, so close to the present day but a bit more advanced. And for the cataclysm I was thinking something akin to a technological collapse, creating a domino effect that would lead the whole previous civilization to come undone completely and utterly with it, lowering considerably the planet's habitability and crippling the biosphere but not to the point of making it forever uninhabitable, just a lot more hostile.
What would be more feasible? Rebuilding/Refurbishing or tearing down as much as possible and recycling?
As for how old the ruins...let's place them at about 100 to 500 years following the collapse, the time needed for the planet to recover with some help the needed habitability to live on it's surface without protections.
As for the technological level of the civilization that build them, let's suppose a mid 22nd to early 23rd century, they were pretty much a type 1 civilization.
Among their technologies there were: advanced nanotechnology (capable of limited self-repair), advanced materials (which made their arcologies possible), robotics and AI (supported by advanced networking and computing apparatuses).
They also employed technologies to control the dynamics of their world (such as weather patterns, pollution and other aspects of the atmosphere, hydrosphere and even lithosphere), which is how the the technological collapse led also to the collapse of the planet's habitability.