I missed that the OP has previously visited Joshua Tree, but don't know when in the year that might have been. In the event this is not interesting, then a second option would be to fly from SAN to SFO ($89) and then drive south to the Monterey Bay area. (The savings on not having to pay a one-way surcharge on the car rental would likely more than offset the flight cost.)
Winter is a great time to visit this area - one can see the migrating monarch butterflies at Pacific Grove, visit the terrific Monterey aquarium and the lovely old Spanish mission in Carmel... But (to me) the highlight would be stunning Point Lobos, the incredible Big Sur coastline, and ideally visit the elephant seals at Piedras Blancas, close to the amazing Hearst Castle, now reopened. On the way south or back north, a stop at the Henry Cowell redwoods near Santa Cruz would possibly leave the OP gobsmacked, as it has for various pals of mine from the UK who experienced the redwoods for the first time. Again, google the places on this map.
https://goo.gl/maps/8GWYLjKMX61kqPBg8
More pictures, also taken in January...
