My experience is that politeness counts. A lot.
I once checked out of an upgraded room (at 7 AM), and listened as a Platinum member demanded that sort of room, screaming at the clerk that he was entitled to one because he was Platinum. The clerk just kept repeating that there weren't any available.
I'm reasonably sure that if the guest had been polite, the clerk would have said that there aren't any clean yet, but one was just checked out of, and he'd have it cleaned as soon as the maids showed up; meanwhile, have a free breakfast on the hotel.
On the opposite side, being polite and undemanding (when a room wasn't available for early check-in) got me upgraded to the Waldorf Towers on a Priceline stay.