Every Wonder would be different in terms of stats given (+20 attack, +20 defense, etc...).  And maybe some rare resources would be given to an alliance bank or player every 24 hours. The stats would be given to every player in the alliances army or whatever the stat is good for.

Maybe have 20 wonders on the map in different locations, kind of like the Tournament squares.  

I have noticed Wonders used in other games and how it has increased pvp.  

However the armies occupying the square would not receive the bonus and in fact over time would get a negative stat to make it harder to hold the square as time goes by.