Put me down on the casual side. Like Mike Moore, I am on vacation at most Nationals so I prefer to be comfortable. Suits are reserved for church, funerals, job interviews, some weddings and business functions in my case. This time after working the convention up till a few minutes before the start of the banquet last thing I wanted was to put on a coat and tie! But, like Jodie said no hat at the dinner table(those undergoing cancer treatment not included). No host is going to impose something that will restrict attendance to the banquet as that does hurt the bottom line and whether some want to admit it or not, the convention is first and foremost a business and has to be treated as such from the financial perspective.
The banquet is what helps make the convention affordable to put on.So in that case it is necessary. Food sales help offset the rental costs and this makes the large venues we require affordable to the society. Without the banquet you would probably see registration costs skyrocket. So while the banquet is not for everyone, supporting it does help keep the convention more viable cost wise.