1.    There is a finite number of them, unlike new construction that just keeps on sprawling.
2.    They are getting rarer. There will never be a glut of old houses on the market.
3.    They are solid. There’s no comparison between plaster lathe walls and sheetrock, or wide-board plank floors and glued-on squares of oak ‘parquet.’
4.    They are built to last. They’re made out of stone and brick and actual timber instead of plywood and 2x4s and god knows what kind of composite and manufactured materials.
5.    They have already passed the test of time by lasting 150 or 200 years through all kinds of weather.  Ever notice how, in a hurricane, it’s the cheap new construction that gets destroyed, not the historic houses?
6.    They have“detail.” Moldings, baseboards, panel doors, plasterwork, marble fireplaces, turned staircase balusters.
7.    They are generously proportioned.  High ceilings, big windows, wide hallways.  (Unless they’re cozy cottages, with smaller rooms and low ceilings to prevent heat loss.)
8.    They’re greener than new houses. Just the act of re-using an old house instead of building or buying a new one saves tens of thousands of dollars, plus energy and resources. Most new construction materials are full of chemicals.
9.    The places where the housing market has tanked are those where the housing stock is made up of new homes, in the fastest growing cities of recent years, like Vegas, Phoenix and San Diego. It’s not just the mortgage situation, but also the fact that the buildings themselves have no intrinsic value.
10.     Old houses have barely suffered in the recent market downturn. It’s the new crap that’s taken a beating in the market.

That last one is based on anecdotal evidence.  Can anyone supply hard evidence of #10?  Or more reasons why old houses (given a decent location) are a good investment in any market?