We currently have a 2400 sq ft, 4 br, 2.5 ba house. Eat in kitchen, dining room, living room, family room, unfinished view-out basement. 2 car garage that hold's my wife's SUV and my tools, i.e. not that big
. We have two kids.
Right now, we have plenty of house. Each kid has a room with the 4th bedroom serving as a guest room/office. But, when my in-laws come down and stay (often) it gets very small. For our family, we probably have borderline too much house. Of course, we plan on having more kids, at which time it will get small quickly. I'm in the process of finishing the basement, which should give us a huge chunk of equity and extra space for guests. Another 1000+ sq ft, 2 br, 1 ba, office, toy/storage room, and family room. Were it not such a great deal, we wouldn't have bought it, but with a little work there's easily $100k in upside to this place.
A lot of it comes down to simple wants. Much of our house isn't used on a daily basis. Formal dining and family room? I go weeks without setting foot in there. Personally I think such rooms are silly, but it makes my wife happy. Personally, I'd rather have another 500 sq ft of garage.
