I check  periodically with stardock to see if there is a new expansion out.
 I totally missed the  Diplomacy expansion.
 
Trinity is just a combination of the game and the two expansions. I just figured i would give a heads up for those who didn't know.
It is available on dvd and download.
This game sells for $40 usd.
 
I havent played it enough yet to know what the real upgrades are in the diplomacy expansion, besides just restructuring of the tech tree.
 http://www.impulsedriven.com/products/ESD-SDE-W006
The link gives details of the differences and you can buy the game there.

I am yet to play this game.  I tried the tutorial and then went back to playing Civ, Settlers and Star Wars RTS.  I should really give this a proper go and then the expansions will likely seem worth the time.

I always avoided this game because I heard it was really complex. But its actually really easy to get into. Ironically all the sins looking games that I tried to play turned out to be much more complex.