Well, not neccesarily , we are quite happy with our 3B home and many homes here have 3 bedrooms,our house is about the same overall size as yours, ie 24 sq's, we made a deliberate decision to have larger rooms rather than a 4th bedroom that we wouldnt use.
You havent mentioned your family size etc so of course you may well need 4 B's but not all households do.
My suggestion would be to somehow pull the back side of the house across so the family room onwards is flush with the kitchen wall; that way your alfresco will flow into your outdoor area, the ensuite will only butt into it slightly rather than cut it off from the back yard completely as it is doing now.
Does this make sense?
I love sitting in my alfresco area (actually gabled verandah but thats another story )and haveing vision of the garden but of course, if you prefer an 'enclosed patio' type alfresco then ignore this suggestion.
Also may depend on where your clothesline is going to go as I guess you dont want alfresco users to be looking straight at washing on the line.