Every kill = 1 point.
You get different rewards for killing X amount in one go as well as X amount total.
400 kills in one map will net you a platinum armour and some other things that come at 100, 200, 300. Then there's something at 500.
For total kills over every mission you will get gold->black fairies until 10k where you get a rainbow fairy.
Also for total kills up to 2k you get an SP shard for every 100 kills and after 2k you get one every 200 kills.

You get no exp or gold for doing those maps. Perfect if you have excess charisma to spend though, if you are close to leveling.