When I drove to Vegas i slept in the car in Flying J/hotel/mcdicks parking lots and I never had any issues. People won't bug you, lots of them are sleeping too. Walmart super centers are also a good choice but they'll be noisier. Bring some blankets too the desert gets cold at night.
Try to avoid I-17 it's possibly the most boring stretch of road ever made. And if you can pick up a radar detector they're pretty cheap and legal there.
Nevada has a lot of ghost towns and Vegas is a definite stop, hotels during the week are dirt cheap. Check out Area 51 too, and there is a town close to it that's made quite the attraction of it but i forgot it's name....
It may be on your way out but i passed by Amarillo Texas and had an awesome steak and saw some caddies planted in the ground
Be sure to bring a toolkit and a lot of music as radio down there is scarce and pretty messed up sometimes