Lusitania
Donor
It was the Wolfram mined in Portugal and Spain that kept the German war machine running but both countries knew it (as well as Britain) that if Germany was cut off from it completely they would be forced to send their troops into the Iberian Peninsula so the British put up with the Portuguese and Spain selling limited quantities to Germany.A neutral Spain does look much more useful. As a conduit Spain was only gradually shut down by the blockade system. & tho the US entry into the war pretty much shut off the tap there was still a trickle into the summer of 1944. If Spain becomes a Axis ally only a few blockade runners can bring material from the Americas or Asia to Spanish ports.
France was also a 'nuetral' from July 1940, functioning as a conduit until November 1942. Turkey was another, tho less useful than Spain. Bulgaria, Sweden, Switzerland, were very minor conduits for Italy and Germany to obtain items from outside Europe.