How's this for a kick in the head....
I needed a hotel room in NY for Monday night...as HHonors, I checked all of the Hiltons (all 4 in Manhattan). No rooms anywhere, except the Waldorf Towers for 1k for the night.
After almost giving up, I figured I'd call the 800 number and see if they had any secrets...they did. Book to arrive one day earlier (Sunday arrival, Tuesday departure) for a two day stay. Bingo! rooms for Monday night available at all four properties...decent rates too.
Very wierd....but worth trying - book a day earlier, and just call and say you missed your flight, but you'll pay for the room and arrive the next day.