I scaled down my expectations based on the posts above and therefore got more or less what I expected.

I checked in at 1:30pm and was asked to come back later because my room was not ready yet. Maybe at 3pm, he said, but no guarantees about the time Furthermore, he said the hotel was fully booked, which is why I would not get an upgrade

Fortunately I had work to do, took a seat in the lobby, connected to the wifi and asked the check-in agent to grab me when the room will be ready. The slow service in the lobby bar was actually fine for me, because I had time to kill. The lobby wifi was horribly slow but allowed me nevertheless to browse - SPG reservations for example. A dummy booking for the same say showed plenty of Wonderful rooms (that I had paid for) and a Studio Suite. As time time approached 3pm, I went back to the check-in desks, now to a different agent. He muttered something like "ah yes, hmm, I will give you someone else's room now..." and voilą - I had been upgraded to a 6th floor Fabulous room

The rest of my stay (requiring nobody's service) has been pleasant: big (750ml) bottle of complimentary water, lights working fine (thanks, MikeBOS!), even the bathroom sink in the middle of the room is OK with single occupancy.