I did this trip June last year for my first JY holiday and loved it. Like you I've travelled on my own previously and get bored with sun/beach holidays.
On this holiday something is happening every day, even the long coach journeys are filled with interesting stops such as Carmel, Monterrey,17 mile drive, santa barbara, Long beach, Calico (ghost town), etc.
Expect a few early mornings and not much time to yourself but its well worth it to see and experience what you do.
Universal studios was a highlight for me we had 7 to 8 ours there and it wasn't enough but to be honest there were so many highlights.
As we went same time of year the tempreture in SF was cool needed a coat/fleece on a night but it gets a lot hotter after that.
Have a great time