Carmel, old mission to look at , lovely beach, nice restaurants, nice shops to browse through, possible sightings of Clint EAstwood ( he used to be mayor), really funny architecture, look like cartoon houses, rich area, drive from here around the monterey peninsula ( private so you have to pay to go in).
Santa Barbara, fishermans pier, nice town, good walks, good seafood.
You really only need to stop about twice in between San Fran and San Diego, the distance isnt that huge. As long as you have a little time in each to expore and along the way there are little gems to find ( literally in places!).
Although since I did once plan a short trip to the States to include a visit to one of my brothers, thinking I could visit him and be back in NY in a day, only to arrive in NY and find he was further, much further, away than I thought, please double check the distances!