Saf Francisco, Los Angeles and San Diego are all along this route. They are all well worth visiting. You can visit Joshua Tree and Palm Springs on your return via old Route 66. If you prefer to take the inland route with a few thousand more miles of driving, you can take in Yellowstone Park and a lot of the canyonland scenery in Utah. A motorhome can be quite convenient, but it will probably be more expensive.
Motorhome rentals are quite a bit more expensive than car rentals.
They use more gas and you still have to pay fees to park them in campgrounds. For two people, a basic car rental costs about one fourth the price, uses half as much gas. Inexpensive hotels, especially if you share a room, can be cheaper than the daily rental premium you must pay for the motorhome. And the hotel staff makes the bed every night. Sounds like a great trip.