Personally, I think driving the whole route would be time well spent, but that is your decision to make based upon how you want to spend your time. In and out of car rental offices and airports compared to hitting the open road with a little less time in the City, no contest in my book !

Personally I wouldn't lose a night in SF, it's a lovely little City and would choose a night along the PCH over a night in LA, but again that's me. Why not go direct to Grand canyon from LA instead of going to Vegas and then having to go back through there on the way to Death valley ? It would save a few miles and some precious time.

An RV will certainly be a more expensive and a slower option which wouldn't be that suitable for the City. They can be great but I don't think in your circumstance.

Being a 'Foreigner', I have not travelled on Memorial Day weekend but from what I have read traffic and crowds can be a nightmare and would possibly be a good time to 'stay put' wherever you are. Someone else may be able to help out better there.