[ip26]

Not the parent comment but 1500sqft roughly gets you something in the range of an ordinary 2br 2ba (waving my hands vigorously on room dimensions, whether 2br 2ba is ordinary, etc). That's most people's "basic/ordinary housing needs".

So looking out from that position, people interested in another 1000sqft are usually thinking of hobbies, exercise equipment, shop space, media room, etc.