I tend to go against the grain w/ tourist advice around here, but I would say that the key to an enjoyable short stay in L.A. is to avoid too much driving. It is a HUGE city, and one can easily spend hours in a rental car travelling to some "must see" thing that ain't all that.
Santa Monica is a nice area but very crowded and not very interesting, IMO. If the weather is nice it's beautiful, though. I would have dinner at Chez Jay, (if you can get in), it is an old-school Steak House on Ocean Avenue. Hasn't changed since Peter Lawford took Sinatra and Marilyn there in '62. Coolest place in SM by far, but then I don't consider most of the newer stuff cool at all.
There are a lot of good museum options, including car related ones, but my top two choices would be the Getty w/ 2 great photo exhibits right now or the Reagan Library which just opened its Airforce One exhibit to the public this week. (You can enter the plane and check it out, used by 6 or 7 Presidents). If I have time, I might be interested in one of these, send me a message. I can also give you more detailed advice on where to go.
As for the Newport Beach advice, yes, there are lots of attractive girls/women down there. They stamp them out on an assembly line. But L.A. is a world class city these days with lots to see, and the idea of going to another county to see hot women is sort of a (?) You could never leave LAX airport and you would see more of that then in most places in the world.
