Interesting that you find the upper deck more private. I find the opposite. I have seen very few QF flights where the upper deck is not 100% full (22 passengers on 3-class or 24 passengers on 2-class), and I have seen few flights where the lower deck is 100% full. So if I am not flying on a full flight, I find the lower density of passengers and the wider cabin provides a feel of openness and being on a large aircraft rather then feeling like the ceiling is curved and low and I am squashed into what feels like a 737 cabin with nice seats.