Day 1 seems real intense! I have done a trip like yours before and SF to LA is a bitch.
I have been to six flags 3-4 times...its alright. Can be super busy and like someone else mentioned, line-ups are long. That area (Santa Clarita) also gets SUPER HOT!! And it is about 1 hour+ ouside of LA depending on traffic. I also found the people who work there very rude....it aint like disneyland.
Drive from LA to Vegas is super easy and fast. I found vegas just ok. I'm not a huge drinker, club lines are stupid long, and shit is not cheap. I probably will never go again. The drive from Vegas to SF...not cool. That's all ill say.
If I were you, SF is such an awesome city (same with LA), I'd just stick to those two....you won't get much outta vegas, unless you are doing the "vegas thing". The time you are going to waste in the car going there and back can be spent else where....plus, do you really want to be exhausted when you come home?
Just my opinion
