In other games, there is always a day in a week that they either have exp buff or drop buff. The experience in game is already fast, but drop rate buff occasionly can boost people to log in more often to farm shards (in game item needed) or farm treasure hunt items or other things they would like in game. Maybe a 50% drop buff now and then wouldn't hurt? Login bonus is great but would they play the game?
Just a suggestion. I played the game for awhile never seen any kind of (free) drop buff now and then.