I have checked in early, or tried and they usually say, we have a room ready for you or we dont. Or if you are plat they would say, we can get you in X room but if you want to wait we will have Y (nicer/suite) open later. I have never been asked to pay.

IMHO, if there is a room and you are willing to take it (might not be an upgrade) the hotel should offer it. I dont see them losing out on anything.