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As far as spotting goes, it can be pretty unpredictable in the city. You might see a P1, you might see nothing at all. Someone once sent me a message similar to this forum post, and I replied with a bunch of different spotting spots in SF, so I might just go look for that.
You're most likely to spot something in the downtown areas of more inland cities like Burlingame, Palo Alto, Menlo Park, Los Gatos, or Los Altos. Santana Row in San Jose almost always has something, but it's about an hour away.
To get a better idea of where I've found cars before, I suggest you check out
my Flickr. I have all my photos mapped, so you'll be able to see the exact locations.
I'd also suggest joining the facebook groups
Bay Area Car Spotters (biggest one),
Bay Area Car Spotters (Regulated) (getting bigger), and maybe
NorCal Exceptional Car Spotters (not so big). Through those groups you'll see what people are spotting throughout the bay area, and also updates on upcoming shows.