Well I'm new to the server and maybe I don't have much of a saying, since I'm still in 'early mid game' so to speak. Also probably I'll just repeat stuff that people before me said but just felt the need to and my 2cents. Personally for me RO was always about two things. Party runs and woe/pvp competition. If you're a player not interested in woe and you have all characters maxed out, then not counting events and high profile runs, there's not much more that game can provide. In this case I understand this perfectly why so many people sit around and uses RO like a messenger.
Personally I don't think introducing more powerful items that old players can compete for is the way to go. It sparks so many balancing issues. In my opinion it has to be something that encourages competition, requires constant tactics change and reward is something that all players strive for. I remember back in 2008-2010 when I was playing RO I participated in WOE for two reasons. For me it was fun party event, but foremost it was all about reading on the forums that I cheat. Cuz it meant I played really well (not that it ever happened, lol ). My point is, that the reward doesn't have to be item or costume in the game. Every type of player has different motivations. That you can appeal to. But yeah. Engaging old players to become more active in game they play for years is extremely difficult task. It's doable but the question is how. Which brings me to another point.
I understand that when you play one game for a number of years, you did it all. You also made connections and friends. You invested so much time in lvling and gearing your characters that it's hard to let go. There's also nostalgia that keeps you going back once you decide to quit. But despite all of this there's simply not many more that you can do. Server needs a steady flow of new players, that eventually will replace old ones. As they grow bored and quit. And sadly there's not that many new RO players. Server needs to attract emaining old RO players, that are scattered across different servers. But this is completely different beast and deserve it's own discussion.
But yeah. Just my thoughts and sorry for broken English. I hope it didn't confuse you to much