I think now the whole upgrade process has become much more structured and rigid. I believe airline personnel used to have more latitude about who to upgrade, and now there are reward account tier levels to consider so that the employees don't get to pick the polite, well dressed, likely trouble-free passengers as much. I could be wrong, but they've tried to monetize and commodify every part of flying, so I'd be shocked if there were still as much power for employees to give something away that could be valued (even just by awarding it to the most frequent flier not already in business or first class).
Count me as someone who does not dress up for plane rides. I dress for the activity I'm going to be doing. Since the activity is sitting in an uncomfortable seat for a few hours, that's my main criteria when deciding what to wear. Slip on shoes, pants with a comfortable waist band (and only pants.... shorts or skirts can get too cold on the long flight), layers. I always look neat and clean and comfortable, but never like the height of fashion. C'est la vie.
Shopper in California's Bay Area