I would argue that mixing is a good idea. 300sqm per household is not a great upper limit for families nor affordable for people with smaller incomes. But houses with 4 apartments of various sizes on 600sqm lots can be quite nice. Add to that single-family-homes with 2.5 stories on similarly sized lots in a 1:2 ratio and you got a nice quarter. If you make the roads broad enough, that is. Feeling cramped in can really destroy the appearance (and take away space for public trees).