True. But it's safe to say that the entire Bay Area, no matter where you live, is going to have its fair share of bad guys looking to jack your ride, steal your scrip and loot and possibly even kill you (or eat you, in the case of the Hellbugs). That's just the world of Defiance in itself (we've seen examples of sneak attacks. Heck, Nolan and Irisa got held up by Sukar and the Spirit Riders, which lead them to Defiance in the first place).
To be fair, it's not just about the car, it's also where you park it. Like I said, the spot I found (map coordinates [1555, 1522], overlooking the Mount Tam area), is a challenging spot to get up to (especially on foot, so no Afflicted hordes or mutants can get up there. I don't know about the 99ers though) and it appears to be rock (which means no Hellbugs can sneak up on you as well, I think). And it has a good view of the sunrise. I say, if you're going to sleep in your car, it's best to have a spot where you feel comfortable enough to park without any surprises.