Captain Jack, who gave us the stats and you have given us developers priorities. I see it as a pretty simple thing to figure out by by asking one question.
What is the goal for opening another server/world.?
Would a new server be focused on keeping veterans happy or would the goal be to attract and retain new players?
If you try and focus on both you may lose both. Veterans will want to be able to bring more than just experience along with them, Like Vane said, it would feel like a waste of 4 years. So if it for veterans, then the setup and development would require new mechanisms.
If the primary goal is to attract and retain new players then really nothing need to change. Simply open a new server. As Mugi stated, new players will always gravitate towards newest/smallest server. This goal would mean NOTHING transfers between servers, otherwise you lose control over initial goal.
The third option here is to leave things as is. I do think with a few tweaks to opening registration page, the selection process at registration, the first 1000 turns, beginning missions, and availability of information, you can increase retention rates.
The question can only be answered by you the developers. What would the primary goal of a new server be? Although all of us appreciate the AWESOME way you involve us in game development, the decision truly is yours. Once that decision is made, the path becomes much clearer.