The high end embassies are for the donors to the winning party’s candidate. The UK, Vatican, Japan, France always seem to go to some knucklehead with money. There is no demand among the monied class donors to be ambassador to say Somalia, Iraq or Syria; career types always get these posts.
Hillary says she's never been influenced by donors, but I bet if you looked at who her ambassadors were for France, Belgium, Sweden, etc. You'd find that they were Democratic donors with little, if any, qualifications.
Before being appointed Ambassador to Japan, I doubt Caroline Kennedy spoke Japanese, had any real experience in or connection to Japanese culture, or anything else that would recommend her as our Nation's emissary to an important ally. Heck, she may not have ever traveled to Japan before.