OK, but I assumed Ψυρρή is also neuter.. and checking with one of the links you gave:
Ψυρρή - ουδέτερο άκλιτο
So not sure why στου Μετς isn't right whilst στου Ψυρρή is. No matter - just what's idiomatic I guess. Perhaps I'd have to live in Athens to 'feel' this. (Yes, I do see though the 'nuance' if Athina is a person, like 'chez', as you say).
As it is, I would almost have expected something like στου Ψυρριού, though it's starting to look a bit odd even to me. I would automatically just say 'στο Ψυρρή'