Your discounting of the possibility of the UAV being recovered fairly intact could also classify as utter nonsense. The damage is most likely on the underbelly during the crash and its quite possible that the landing gear and the optics etc. were destroyed which likely explains the reason as to why the Iranians have not provided any footage, photos of the underbelly of the aircraft.
The real question is not what they have gained, it is rather what they can do with it. Very many fairly clued up folks on the US side are concerned by this loss. Maybe the Russians or Chinese would be included in the reverse engineering.
With such type of operations, loss of this nature is very much a possibility and is not unprecedented.