diplomacy would require the unity of one ecconomic power. That is if they were to have one, legally binding for all 25, voice. This would allow ecconomic sanctions/rewards to be more efficiently used. It would also make it far more possible to make the euro the world's reserve currency and the eu's bully stick.
I think I see what you mean. I was under the impression that the EU would be able to control any currencies the member states used, but it would be much simpler to have only one currency to control- centrally.
I'm interested how the Eu intends to control dissent among the members on issues of foreign (and domestic, I suppose) issues, especially if they were to have a 'unified' voice in the UN.
What happens if there's another Iraq (such as Syria or Iran) and some EU members want to go in and some don't- how will they represent their position to the UN council, or to the rest of the world, for that matter?