Another reason to go after north Africa is the potential to put pressure on Britain by trying to push toward India, India is key to Britain/USA fighting against Japan and if Germany can push toward India from one direction and Japan from the other, who knows.
If India fell to one of the axis powers, Japan could then go into Russia from the East/South East, while Germany goes in from the west, while Britain is still active in India/Asia it would be a risk for Japan to try and go into Russia.
It is imperative that sober thought be a requisite prior to the strategy mentioned above. Germany will simply not have the resources necessary for an advance against India until Russia is vanquished. Russia will not be an easy pill for Germany to swallow.
"Many, who should know better, think that wars can be decided by soulless machines, rather than by the blood and anguish of brave men." ~Patton