A few pointers, IMHO...
1) While mentioned by someone above, water, mold, mildew damage from Sandy should be a bigger concern.
2) Overall size is certainly important. However, the location of your walls, stairs, doorways, HVAC, etc. are equally important. Usable square footage may be what to look for.
Folks with "upstairs" layouts can go through walls if necessary b/c they're typically made of plaster or dry wall. In a basement, especially an older one, the walls will be concrete or cinder block....so you can't really go through them.
You must now also face the ultimate dilemma of O Gauge Railroading: the choice between wide, realistic sweeping curves or smaller curves that will give you more layout options. As I get older, my railroad curves (and myself) seem to get wider.
