I have to say that I have had very good results with upgrades this year. Last week I was upgraded to the Presidential Suite (my first presidential suite upgrade with Hilton and I suspect my last).
A few weeks ago I had a 2 night stay and, on the second day, decided to go home. Came back to the hotel at about 1:30 and asked if I could go without charge and there was no problem at all.
Bobette