The main issue for me was people strategizing on how to best set their alliances up geographically in time for world wonders at the start of servers. This led to redonkulous amount colonizing and alliances trying to consolidate their cores instead of invading other oceans to take down rival alliances. Easiest way to fix Grepolis is removing colonizing and conquering ghost towns from the game altogether, if the only way to get your next city was by conquering another active player, it would feel lot more like war game instead of some sim city rip off.
This would in turn bring the active population of the server inwards to the core keeping the server active for longer and bring back the concept of "rimming" players back to the game, which is greatly missed.
While a end game is important, I think it is also important to acknowledge the achievements of the alliances that dominated the server while it was at its peak, having gold, silver and bronze milestones for alliances strive for will create additional competition and more fairly reflect who the best alliances on a server were when all is said and done. Only once all milestones have been reached or 3 years has passed that is when age of wonders should kick in.
If you guys disagree with me, that's fine but figure out and vote on what is the single biggest issue effecting Grepolis and demand that be fixed first rather than pointing out 100 of things wrong with the game at the same time, as the will not get you nowhere with the people that have devoloped this game and see it as their baby.