Well Zazo...,
Hard to tell...
Yes, it has happened that during restoration of some of the spare wheel well cars the spare wheel well was removed.
Once because the well was just not rarely rusty or bent, otherwise because it is easier to replace the whole trunk floor (due to surface rust) without the "hassle" of keeping the well. Maybe also the one or other owner wanted the larger tank. Hard to tell...; this surely were individual decisions.
Personally, I would not want to have that one removed - although I do not like the looks of the well from the outside very much. Personally, I think the car looks nicer without.
Achim