I"ve often thought that Evony could keep things more interesting by making this a round-based game. Let each round last 3 months (so 4 rounds per year), and make it a race to the top, with small prizes (game coins or something) for the top ten alliances and players in each category.

That way the older servers would never really die out from boredom, because every 3 months everyone on the server starts over as a beginner and has the challenge of building up and becoming a winner (top ten) all over again. It would also allow for those who got off to a slow start in their first attempt to improve their game with each round - and for friendships/established alliances to remain intact instead of losing people to new servers when they get bored.