Can meshes be cloned? For example could I import one house and then create several instances?  I would assume the answer to be yes, but I just wanted to confirm.

Yes

Mesh.clone();

I think it’s still the same in 4.X ^_^

Using clone is a bad idea. You then duplicate the entire data. Your project will be bloated and will perform poorly.
instead do:
var baseHouse:Mesh = new Mesh(geom, mat) or from loading it or from as3.

for(var xx…
  scene.addChild(  new Mesh( baseHouse.geometry, somemat or baseHouse.material )

Another efficient way to proceed is to build houses per materials, and loop over them. per loop finish with a Merge. Handle next type of house material.

mmm. I thought Clone was the best way if you needed to reuse the same model a number of times for, say, collectable items in a game?

Question is: what do you want to “collect”: A full data copy of a house or a copy of a house? On screen they look the same.
Use clone only if you destroy/alter the geometry of the shared house data.

point. ^_^