Resources are protected according to station level. When players' resources are over the protection limit, you'll steal resources. As for debris drops, it depends on how many ships they have in their station. When the ships docked in their station are over a certain limit, they will convert into debris drops. In general if you attack active and strong players, you will get substantial drops and resources stolen.
The defender's space station will become heavily damaged in the crossfire, destroying a lot of the resources stored. For this reason, the attacker is only able to get away with 50% of the resources lost by the defender.