Make little "easter Eggs" with the names/ profile picture of each MOD in the background kinda "hidden" (but not really) as well as maybe some of the most active/communicative players on the forums as well.
Also, as the World progresses, have the background start of as the construction of a city, once about halfway done with the world, show the background to be myth units and troops and boats on two different sides like they're going to war. Then, towards WW time, just a week before or so, change the background to any of the WWs. Then whichever alliance wins the world, have their alliance name displayed in the background for all to see saying "Congratulations to x alliance for Conquering the world!"
Then in addition to this, during each event, have little "Easter Eggs" of the events in the background as well.
So here's an example (hypothetical):
Oropos is in WWs and it's Christmas time. The background would show the Lighthouse of Alexandria with a little Santa hat on top and in of of the windows is the profile picture (for the externals) of my account (as displayed with each post) and/or Antz2013's and/or Figtree's pro pic or even Medic911's (littered throughout various windows).
This way, it gives the graphics team a fun job and keeps them busy while also providing entertainment to the external readers of seeing a "cool background" (and you best believe it'll be a topic of discussion) while also providing good info for players who'd like to join in late in the game so that they'll have a clue as to how far along and "intense" the world will be before joining.
As far as the forum itself, just so long as it's user friendly and what I call "baby proof" (being that pretty much a toddler can figure out how to navigate the forums), then i'm good there.