Welcome to the forum! :-)
I personally wouldn’t use this plan as Germany, for various reasons:
1. I’m not a big fan of a Romanian complex and believe that the money is better spent on buying units. Spending 12 IPC on a complex that would only produce 3 units a round when the major IPC in Germany is just one area further away from the Russian border, just doesn’t sound attractive to me. For example, suppose you would at one time buy 10 inf in Germany to support an invasion of Russia, consider that for only 10 IPCs extra you could have bought mechs that will quickly outrun any slow units you can buy in Romania.
2. The UK will not really feel threatened by this purchase. While ‘Sea Lion’ (amphibious invasion of the UK) is not generally the best option for Germany, it’s a good thing to make them at least worry about it.
3. Like Hunter Jones said, you’re giving the Axis a lot of extra units. It’s not just South America, but either Russia or UK Pacific will really be helped by the four Afghans, and units from various other true neutrals will also make their presence felt.
4. The big one: the US player will just love this. Spain is an ideal beachhead for them - see this thread: http://www.axisandallies.org/forums/index.php?topic=38126.0 for a discussion on the Allies taking Spain for that reason. German forces in Spain (and Gibraltar for that matter) will be precisely one move away from the full might of the most powerful allied nation. Once the US enters the war, Germany will have to defend against them before you’re even close to Moscow.