Regularly pestering the (very nice) chairperson of the board of my condominium about #EnergyEfficiency definitely achieved something. Thermostats were installed on all radiators for this heating season. Heating costs went down so much that our monthly fees for December were completely cancelled. I keep the thermostats at level 1 (out of 3) and my apartment is now at 16 °C. Last year I was often at 22 °C even with all radiators off, due to overheated staircases and downstairs shops.
The staircase is still at 19 °C so there's still room for improvement. It should be 17 °C tops. We can probably reduce our heating by another 10 % with some simple tweaks in the pressure etc. (planned for later in this season, IIRC).