I think the proportions of the buildings look great. I assume this is a diorama or static scene rather than a piece of wargames terrian? I'd be a bit concerned with the strength of some of the foam pieces otherwise, but would assume that you could (carefully!) push wire into the thinner forms to add strength.
One thing I'd be tempted to do (after a small test!) is wipe filler into the gaps between the 'stones' in order to hide crimes and provide a mortar texture. I've never tried this myself, it just occurred to me looking at your work.
Great stuff!