First of all.. that Yamamoto quote has never been substantiated and the are far more complicated reason why tiny Japan wouldn't want to stretch supply lines(you must have heard an officer or two talk about supply lines when you were serving lunch in the mess across the Pacific. They were already spread out across Asia.
You also might not have noticed but the world has changed in the last 70 years... The idea of a militia also implies that people receive some kind of training and have minimal discipline. That is the case in Switzerland where you don't see the kind of insanity that happens in the US.
By the way, some tin foil geniuses also said a similar thing about Germany not invading Switzerland... It's always good for a laugh...
Anyway, Admiral Yamamoto would today probably say something like "why bother invading? Let them keep killing themselves"