I always kill them no matter the level. If they are in Durotar (and I have time) I will camp them/ guide them all the way back home, even if it is a low level.
If theres something halfdecent on tv and I got nothing better to do, I treat the lowbies venturing into durotar as rare spawns. Even if they logged and came back 2hs after I would still be there waiting for that loot. Can be quite fun sometimes when there are a decent number off them, just patrolling back and fourth while watching the hunter tracking.
Bit fun to make them believe you wont hurt them either. Just look at them long enough eventually they do some gayfag emote AND then you kill them.
In any other case than that I wont camp low levels, I would just kill them once and move on.