Your trip sounds good, but a little too clustered around the SW to me.
- Do LA for a single day and one night so you can experience some cool bars, then leave.
- Santa Barbara is good for 1-2 days and you can drive north into the hills for some lovely scenery and good food.
- San Diego is great and I could easily spend 3+ days there. I highly recommend Marriot Gaslamp. NEarer the edge of the gaslamp district, but overlooking the baseball stadium and has a cracking open air bar on the roof, which you don't have to queue to get into on a busy night being a hotel guest.
- Santa Monica for 2 days would work as you can wonder down and spend a day chillaxing on the beach down by Venice. Plus this should be your last stop as it's only a 20min drive to the airport.
Or head back to Vegas and make the trip a little longer. Our 2nd trip out there last april consisted of:
1. Stay over LA (flight landed 8pm ish).
2. Drive to Laguna Beach (1.5hrs - lovely place, the gf and you both will love it) and spend day + night here.
3. Drive to San Diego (1.5hrs).
4. San Diego.
5. Drive to Vegas (6.5hrs)
6. Vegas.
7. Vegas.
8. Grand Canyon Day Trip.
9. Drive through Mojave Desert to Palm Springs (6.5hrs) and party.
10. Drive to Santa Barbara (5hrs) - Party and chill.
11. Santa Barbara relaxing and driving up into the hills in the 'Stang!
12. A short hop to Santa Monica, staying at the Georgian, relaxing down at Venice beach. Close to the hotel we highly recommend 'Bar Pintxo' (bar/tapas), it was amazing and the better than most Tapas the GF had when she lived in Spain!.
13. 1/2 day relaxing in Santa Monica before short drive to LAX and home.
Don't just limit yourself to hanging around LA and the SW
