Add the ability of upgrading small buildings to large buildings with coins.
Sometimes, things just change. For example, stations expand, units are re-allocated eg.... When I have been upgrading some of my fire stations to have CAS's, I have ran into an issue of not being able to get the ambulance extension on small fire stations. I cannot really justify paying up to 750k per upgrade for a single ambulance.
I know I always could just create a new ambulance station but it would be nice just to have a single station.