score:7
the main benefit was not getting the government arrested and replaced by others who were more likely to do as they were told by the USSR.
The GDR government was under a lot of pressure from Moscow to "do something" about the flood of their citizens fleeing to the west.
That flood of refugees, most of them the brightest and best educated of the country, was also seriously affecting the economy at all levels.
So putting a stop to it, in a command economy like the Soviet style system the GDR employed, was paramount.
And of course they portrayed it internally as a system to prevent intrusion by imperialist capitalist forces, a great patriotic work. Which kinda worked (though there were of course always a group of malcontents who wanted out anyway, no matter the amount of propaganda poured into them).
As to foreign trade, there was not a lot of that anyway outside the Comecon and Warsaw pact, the wall had little or no effect on that.