Stuff usually makes sense within context, there's lot's of buzz for example on Twitter about how some old stuff was beautiful and the new one is ugly. They are doing this for political propaganda and money but there's a reason why people tear down the old "beautiful" stuff to build the new contemporary thing and when doing it they thought that the old stuff was bad for one reason or another. Some day in the future people will be preserving some all glass facade building for it's significance when everyone else has moved to this new thing.
The historical significance is just one thing though, sometimes people preserve stuff for any reason. Sometimes, people preserve stuff because it's amazing that someone did this even if it's not a masterpiece in any way - like the restored version of Ecce Homo :)