Some suggestions:
-New NPC
Last year I played on a server that had an NPC which sold items like skill eraser (the green orb thing from item mall), skin change scroll, instant return scroll, basic avatars (mostly the not so popular ones) with reduced blue capacity and few other things for gold. Mainly things that people usually don't buy from the item mall because they obviously cost and are not that useful.
This would be a nice addition to your features as it would decrease and slow down the inflation and let people have more fun. No one buys the skin changers from item mall because it's not really worth to pay real money to get a slightly different look for your char but when it's sold for gold, a lot people try new looks. Same goes for the skill erasers, if a player wants to wipe all his skills, he'll just buy a skill reset scroll instead of them. If someone wants to remove 30-90 mastery/skills, he'll rather collect hearts than pay real money for it and collecting hearts certainly isn't that fun.
-DS
Another thing which I would like to see either in the shop or in the uniques' drop lists is 5% devil and extension gears. Me and many others love the effects/looks of devil/angel spirits and it would be completely fair situation for everyone when it's only 5% and not bought by silk. As drops, they would also provide a nice way to make some extra profit and increase the activity in the area where they can be obtained from.
-Battle Arena
Lastly I would like you to reconsider enabling BA. I heard that you're afraid of cheating. You can decrease that to minimum quite easily. Make a clear statement that it's not allowed to go AFK in BA and anyone doing so, will be punished. Make it very strict, like 2 strikes and then you're gone. Encourage people to report cheaters and give them credit for doing so. All they need to do is to take 2 pictures during the game of the player standing in the respawn zone. That way it can be proved the player was AFK because: A. He hasn't moved at all. B. His name isn't on the scoreboard. C. He's still in the respawn zone after the game has been running for X-minutes. Haters can of course try to false report their enemies if they don't have high enough score to be shown on the board. It'd be best if the list could be extended so we could see who has 0 score or extremely low score. Anyways false reporters aren't that hard to catch because only stupid people would take such a risk. Have someone from the team check the respawn area every now and then during the games and let people know that you are keeping an eye on it.