Very interesting piece. A lot of good points have been raised above. From the interior shelving insert, the safe appears to be a document safe (can't think of the proper term) rather than a valuables safe, but that doesn't mean the previous owner didn't use one for the other. It'd help if the thickness of the door was shown. Walls look pretty thick, dunno the thickness of the steel.
Besides having a working combination and the weight, another important factor is dimensions. Without having a weight, it's unknown if it could be safely put on a modern floor. However, the bigger question is can you get it in your building?
So far as defeating it, pros would wheel it out to a truck with lift gate and peel the door at leisure. Possibly concealed as a moving company. The teens down the street wouldn't bother.