There is a lot of discussion re the issue of representation of the EU with either a "singe voice" vs (latest idea introduced)"single mouth" (eg in the G20).
IME what is key is for single EU voice and/or mouth to reflect a position that's representative of all 27 or decision reached by 27.
Is having a single mouth boring? No, IME that is not the case with European PMs and Presidents (eg Sarkozy) or Obama when they speak re national interest
Thus IMO the challenge is to define "EU interest" in an inclusive way for all "parts" of the EU, in the same way that eg Angela's voice is inclusive of all 16 laender & Obama's of all 50 states & Brown's of England, Scotland, Wales and NI.