Think about the padding. Many time padding can reduce leg stress and minor back pains. So yes carpeting is critical to a booth.

Take a look at this article about padding it may help. Trade Show Flooring, Save Thy Feet

Those are good questions, I find that many exhibitors opt out of getting carpet for their booth if they know that the hall is already carpeted. And you can use that knowledge to your advantage. The whole game about going to trade shows is to get your booth noticed. Adding nice padded carpeting to an otherwise dull show floor is going to make your booth really stand out from the crowd.
Plus you may get more people wanting to mingle just to rest their tired feet. Colors? Lets see if anyone else has any comments there.

Visqueen is the clear plastic that the decorators put over your carpeting after they lay it down. It is pulled off just before the show starts and yes you need it, unless you don’t mind fork lift tracks through your booth space, especially if you have a corner booth.