I wouldn't waste my time going out of my way to visit Apple HQ if I was visiting the Bay Area. There's a million more interesting things to do around here.
I couldn't agree more.
If you like cars and people watching, then Rodeo drive is worth a spin for plenty of both.
As TheAnswer pointed out, the Third Street Promenade is always interesting too - that is besides the Apple store there.
Free museums worth seeing are the Getty in Bel Aire and their Villa in Malibu.
As far as amusement parks and roller coasters are concerned, no spectacular ones here in LA, but still fun if you have the time and the money. They're not cheap! Just make sure that you get there early and it's preferable to go during the week rather than weekends. As Bob Barker would say - come on down and you'll have fun