Nice ideas I'm getting here. Looks like a few groups could take up careers in urban renewal if adventuring fell off.
Now here's an interesting little fact for you arsonists out there. Everything has an ignition point. Yes, steel will burn.
Another nasty trick to pull on the PCs is to have them roll for their equipment, even if they made their save.
Oh, and the bad guys can always try the same tricks the players do. Such as a dragon that burns away some supports to bring down the house on a party.
Though for real fun there's nothing like having the place fall down around everybodies' ears all on its lonesome. As far as the players can tell.
Which gives me an idea. Would anybody be interested in doing a book on environmental hazards? Maybe for ENWorld Publishing. A book covering the various things that can happen thanks to damage, neglect, and/or stray Acts of God