The last two times we've gone to SoCal, for my brother's wedding in July last year and to DL/Palm Springs in November, we flew in and out of Vegas because it literally cost us
$800 less than flying in and out of any of the LA area airports (including the difference in price from the flight and rental car.)
I have to agree with Magic, there's really not much to see along the way. We got in at 1am and stayed at the border. Primm and Jean both have hotels. There's various rides and an outlet mall.
There's long stretches of that road that are pretty desolate. Nothing for miles and miles. We actually had to pull off the interstate and let the boys pee on the side of the road!
In Barstow, theres another outlet mall, and there's a nice in and out burger (I love in and out burgers!) and various sit down and fast food restaurants.
If AT ALL possible, refrain from driving towards LA on Sunday, frankly any time on Sunday, and from driving towards Vegas on Friday (though if you leave early in the day it isn't too terribly bad). You will start to get back ups going into LA a good two hours out (two hours being pre-congestion time) and going out of LA it will be a grid lock much of the way to Vegas. When we flew to Vegas last time, it was a Friday and as I mentioned it was 1am. When we drove to the border we saw the cars lined up still at 2am (which is about when we got all our stuff and made it to the border.) Both times I drove back to Vegas on Sunday and you would not believe the traffic I saw going back in to LA.
Good news, on a typical day avoiding rush hour, it should only take you about 4-4.5 hours of drive time.