As you only have 5 days in San Francisco (Very cold in September) I wouldn't drive that far. It was Mark Twain who said "The coldest winter I ever spent was a summer in San Francisco" .I went south to San Simeon (Randolph Hearst's castle) about 3.5 hrs away and ate in the local town where they serve the best Pizza I have tasted. Santa Cruz is a possibility but not to my taste - nice beach, dilapidated but characterful pier where there are loads of vagrants or go down as far as the Big Sur and Carmel (Clint Eastwood was the mayor) on the 17 mile drive near Monterrey only a couple of hours from SF. PLenty of places to visit if you drive south on the Pacific Coast Highway (Highway1).