Silicon Valley isn't a city. San Francisco is. I don't know whether Jacobs wanted to encourage such factors --- she turned city planning on its head with her book in 1960, and it was a data-driven book, while the orthodoxy at the time satisfied "The urbanists are merely one group who hasn't figured out that when an argument suggests/implies behavior that doesn't happen, the argument is wrong, no matter how appealing the proponents find the conclusion or proposals."