Yosemite NP is simply amazing. I agree that you should stay in El Portal and probably take advantage of Yosemite View Lodge. It is very close to the gate of Yosemite NP. Perfect for getting to the valley floor. You probably won't want to make the drive to the Mariposa area if there is alot of snow on the ground.
Be careful if you decide to fly into LA and then fly out of SF. Rental car companies typically charge you a HUGE drop off fee for doing that. Sometimes as much as a plane ticket. Keep your eye out for that.
Hope you have a great trip!
I have some good pics of Yosemite View Lodge if you would like to see them and the surrounding area up there.
Where do you plan on staying at DL?