I've found upgrades to be a lottery. No upgrade when full (fair enough), upgrades to the 2 bedroom apartment rooms, upgrades of two categories to the exec rooms.

Having now done the standard, deluxe and exec rooms in the past few weeks, there isn't that much of a difference overall besides a little bit more space and a slightly more modern room. In many ways, I prefer a decent corner standard room to an exec room. The 2 bed apartment was a bit excessive for a 10 hour overnight work stay!