I'd like to be able to kill people in their sleep without alerting people near by,
Yeah but... why? For the XP? For their gear? Or just for the lulz?
The only time when I could recommend taking the Sandman perk is for the latter. When you basically want to kill people silently in their sleep because you want to kill people silently in their sleep, as opposed to the killing being means to some other end.
Actually, now that I think about it, people do go to bed in Goodsprings, The Correctional Facility, Novac, Camp Forlorn Hope, Camp McCarran... just wait until midnight, then if they are not automatically in their beds wait around for them to walk there and hop in. What particular place were you wanting to kill people in?