Add something original.
Now hear me out on this; this is a very difficult thing to do but might bring traffic back in. I suggest you take a team of coders, and make a plugin that is entirely original, something people will be hard-pressed to find anywhere else, like but in ghosts, to where when you die, the player is a ghost, which needs to be revived, i think that would add a good layer of co-op, so one person couldn't just run out there, but might have to slow down for a bit, and possibly bring a friend to the mix. This also helps with the consumption of items. I don't know if everyone feels this, but I am stacking up on items, too many to handle. So I think it may be a good idea to make a structure for every time someone dies, they could be revived with that somehow. People might think twice about PvP, ultimately coding the rage-quits in half. And might bring a bit of suspense in "How long will it take me/my friend to get revived?". And if both of them died, they could bring more people to revive them, or ally with others. This is only a suggestion for more co-op play style, and could possibly bring more traffic.