What makes a game fun is aiming for certain goals and achieving them, and that is where this server is lacking.
The only reason people play the 562, with all of its glitches and such, is because you are not just handed everything; you have to work to get better armor, & weapons (even though most of them are useless at the moment)- at least, that's why i played the 562. I wanted to get the hand cannon, ags, and so on.
Since this is a Pk server, I'm not going to tell you to add trainable skills and what not, however you could add special items that you can only buy when you have a certain amount of kills or pk points, similar to the 562. I know you don't have the interfaces you have in the 562, but it would be much simpler to make in the 517, all you would have to do is add a npc shop, and restrict some items from being spawned.
Possible shop items:
Fire Cape, Rune Defender, PvP armor/weapons etc
Unique items for your client, i.e. "dragon whip"
Please consider it, thanks.