San Deigo is a really awesome airport. I've flown into SAN
like 200 times already since my familia lives in La Jolla and when I was living in Virginia, I had the pleasure of flying to San Diego monthly for a weekend visit. As for spotting, there is only one legal spot, which, as mentioned, the parking lot. There are several off-perimeter spots, such as Balboa Park, but you'll get the normal "boring" shots of the airplane and sky. Another cool spot is the residential area on top of the hill, which is awesome, but it's more "watching" then taking pictures becuase it's fairly far away.