I feel a second banner flight has substantial value and would show we're serious. One hit wonders are too quickly forgotten. The majority of the press will happen in the days following the game giving the fans enough knowledge to be looking for it, and talking about it, prior to flying it the second time around. Ideally this would maximize exposure. If they happen to bench Cassel at the half and we cut it off to "We deserve better - Fire Pioli" the next week, it will make a pretty bold statement.
I would not see a point in a third flight but, as AustinChief mentioned, at that point it needs to change to another avenue of exposure to give the media the opportunity to mention the ChiefsPlanet goons have called an Omaha and are now running a billboard straight up Pioli's ass.