When I moved into this house there was a second floor that was only reachable by a stairway in the bathroom. You had to climb over the toilet to get upstairs. I knocked out some walls, moved the bathroom and put a spiral stairway in the living room. I loved it.
Later, after we had paid off the first mortgage, we refinanced and put a conventional stairway in the house. It takes up lots of room and does not have the charm of the spiral stairs.
I saw this stairway today. Someday, I hope to have another house with a spiral stairway, maybe this one. The tilted center pole helps make up for the wasted space that spirals have under the treads.
There are many situations where a property can be enhanced by creating a usable space from a redundant upper level, however a consistent factor is limited space. The introduction of a staircase to provide access to a proposed upper level will invariably compromise the floor space below where originally no stairs was intended.