I tend to see this as a much more mundane affair. Hitler, as an aspiring artist, was very much inclined towards architecture, evidenced not only by his numerous paintings, but also very strongly by the fact that he was actually recommended to get into architecture by the Vienna arts academy when they rejected him (ahem, for 'lack of appreciation of the human form', or something similar).
So, megalomaniac fuehrer + architect-dilettante + his many suck-ups like Speer = Germania.
You can't blame him for the autobahns though...