This post made me think of another factor. How many days a family needs could depend on how far they live from DLR which affects how often they can get there to visit. It takes a 4 hour plane ride for us the get to DLR and we usually only get a trip to DL or WDW once every 1-2 years. That fact makes us want to squeeze as much Disney enjoyment as possible out of each trip. If we got to go a few times a year, we would probably feel differently
Oh, and we miss the 6 day option too.