I recall KGB writing something about ruins being their own terrain type, and giving certain units (like the ghost) a bonus there.
At the time, I thought it wouldn't have much impact on the game..and (although a neat idea) probably wasn't worth the trouble. But, i have recently been having a number of battles on the sites of previously razed cities...and I though to meself "why not lump ruins and razed cities together into a single terrain type"....then you could give some of the nasty creatures (demons, undead, devils..orcs?) bonuses in that terrain. So, now these units gets a strength boost for hanging around cities they raze...giving them an incentive to raze cities and generally behave malevolently.
Anywhoo...hardly a game changer, but it seems like a nice thematic touch.