The San Diego area is really nice and it is only a 1 1/2 to 2 hour drive depending on where you stop (it has taken us that long to drive to and from the Universal/Griffin Park area to the DLR area with LA traffic so I would say either direction could take you the same amount of time even though LA etc. looks closer on a map).
I agree that the Newport Beach/Balboa Island area is fun and nice and Laguna and Crystal Cove are also nice. There are a ton of cute beach towns between DLR and San Diego. Coronado Island in San Diego is very nice-- there is a beautiful beach, a historic hotel and lots of little shops and restaurants and places to explore. There is a lot you can do in San Diego like Harbor Tours, the zoo, visit Old town, etc. I will say the Coronado beach is a lot bigger and sometimes more crowded than some of the smaller areas up and down the coast. We enjoy the California feel of a lot of those smaller beach towns. We have friends that live in the Carlsbad area, so we have spent time there, at Del Mar, Encinitas, Solana, La Jolla etc. They are all fun places with good beaches and fun local shops and restaurants. There are a lot of places to explore.
If you go north, the Warner Brothers Studio tour is great, but if you aren't into the Hollywood type stuff, it might not be the right fit-- Griffith is beautiful and wonderful to see, but if we weren't going to Universal, Warner Brothers, and weren't that interested in typical LA or Hollywood, it might not be worth the drive and traffic for just that. Going south from DLR is much more relaxed and laid back than heading to the LA area in my opinion.
We often arrive at DLR on a Saturday and them leave on Wednesday afternoon and head south for a few days.