yes, in theory a tradeable currency would be useful for between gamers... but what else could it be used for? I mean ya, i could say "here, 50k Dawn of Fantasy coins and you can protect me for a week" but really, i think just making the resources in game tradeable would be a more likley option.
1) It allows players to gain more use from the resources
2)It doesnt force the designers to create more complicated aspects or rewrite the game's economic structure by bringing in another currency
3)If the designers were to create this new currency, then the players would need a way of getting it and a way to spend it. This could lead to a game-wide rewrite, to institute a new resource, resource gathering objects/people, and then items or re-write the costs of items to spend it on.
All in all-im not saying its a bad idea, a good one actually-but when you take everything into account, it almost wouldnt be worthit. though, then again, i havent played the game yet so im not absolutly clear on how the whole system works.
Keep up the good ideas!