I haven't played as NS yet, but in my most recent game I got them into the Axis pre-Danzig and sent one Armeekorps of three '39 infantry and an extra single CAV to Spain in March of '39. I assumed MC in July and moved 80% of the Spanish army onto the French border and the rest around Gibraltar with the Germans. September 1, 1939 and the war started. Gibraltar was in Spanish hands by the 3rd and not only did I keep 20-30 French divisions tied down on the Spanish frontier, but I actually advanced a few times! On the down side, the Spanish overseas territories were lost with all of their defenders by January of 1940. I tried to keep them fighting, but the British and French went wild with invasions! Until I defeated France in May, Spain only held it's Continental lands and Gibraltar! However Spain committed dozens of divisions to the war in Afrika, Russia, France (and it's garrison) and Sealion in '44 has been their most recent involvement. They have a terribly outdated navy, but I used it to great effect supporting the war in the Med and tying down ships and invasion landings during Sealion! They have been a necessary force in all of these theaters. And that is just with MC!
Normal/Normal and with 90+ divisions and 180 manpower! They have recovered all of their lost territories with minimal to no Axis support and provided the first three, non-para, infantry units to land in England! With their own ships! So, without forts, infrastructure builds or a modern navy, they have cemented themselves as an equal to the likes of Italy! I give them blueprints for industry and units, but the reinforcing and building is all AI. They sent three sets of 3x lvl II FTR's which were cruicial to protecting Brest, Paris and the Bay of Biscay during the '42-'44 Allied Air Campaign over Europe! 2x Veteran armor divisions splicing through Soviet lines during the harsh Russian counter-attacks of the winter of '41-'42! Gosh. Franco really bailed us out! Thanks man!
I did see the Allies air and naval-air attack the Spanish port at La Coruna a few times, and, because Portugal was also in the Axis before the War, The Brits landed at Faro in mid-late '40, but were quickly driven back into the sea by Spanish reinforcements!