eh homie, sunset beach is pretty sick. the weather has been hella warm lately, like 70-80 degreez during the day, but.....at night, even in the summer time, you will be hard pressed to find a warm night on the beach, may aswell be bodega bay. it usually cools off at least 30 degrees, especially on the water. it may not be the best idea to stay on the beach for the night.
in watson, you never really see cops all that much on the beach down there, but i think they are more strict about bon fires and people being on the beach over night, but that's if they even check.
in santa cruz, the beach just south of the boardwalk is nice, but again, it won't be all that warm. i think you can stay there all night though. and you can build a big ass bon fire there, you will prolly see alot of people out there if it is nice out. alot of hippies stay in that area, so they got bon fires and shit going alot, but they my only allow that seasonally, i have never kicked it on that beach but like once during the day time cause there is no parking around there.
let me know if you have any more questions homie