i'd also add, maybe velocipede with it being a somewhat local dealer is a good thing.
according to dahon, there are about 4 "resellers" in maine, though they aren't likely to have any in stock. you might talk one of them into getting models shipped in for demo rides.
you were right, harris cyclery in boston isn't selling bike fridays anymore. strange.
3 flights a year isn't worth getting a brompton though. if you think having it in your car trunk, without ever having to remove it to make space for other things, would cause you to ride your bike more, then its wrth it. in terms of using a car, i get so lazy about folding that i put my bike on a bike rack instead.
i also am intersetd in getting an s&s bike. i want to get out there and see what steel bikes i like first. if i can make it convenient enough to separate quickly, i might forgo my folding bike in the future.