It depends on what you want to see and what your interests are and how much you want to spend.
I love San Diego; but that's because I have family living there and we keep going back to stay with my aunt and her family; and having the opportunity to see different things. So if you decide you want to head to SD, there are things you could do there with the family.
Alternatively, it is nice to spend time around Huntington, Venice, Seal, Long Beaches and/or maybe Santa Monica pier. There is an aquarium at Long Beach; or you could do a gondola ride (I think they are an hour or two) around the Naples canals and then head to Seal beach.
Alternatively, you could head into LA proper.
If you're after a place to get out of the city and see a bit of the countryside, then maybe a drive towards Julian, look at the little country town and have apple pie with the potential to stop at the San Diego Wild Animal Park might be something you could do. Julian isn't wildly exciting but it's a cutesy little country town and the drive is quite pleasant out.