Has anyone ever upgraded to business class after arriving at the airport? If so, was the extra seat/leg room/privacy worth it? I would never pay full price to get business class, but upgrading for $40 a ticket might be in my budget -- if it's worth it. We are a family of 4 (some of us pooh-sized) and would love to sit 2x2 (only available in business class). Thanks for your advice!