provisionally, i admire david cameron's go-it-alone approach with regard to europe. i wouldn't frame this in terms of sovereignty myself, but rather just say that, other things being equal, i'm in favor of balkanization, fragmentation. it's hard not to realize that though the euro had some good effects there for awhile, when the thing starts to go bad, you are at the mercy of forces completely beyond your control. surely merkel is having that sensation, but so is the government of greece. the problem with centralization of huge swathes of geography and economy is the extreme distance it imposes between individual and community will and action and the actual decisions that affect them. the more distant power is from all the sites over which it operates, the less accountable to any it can possibly be. one loses all control at the level of multi-national bodies over one's own fate, and one loses all responsibility.
'sovereignty' in this case is an alternative way of saying that. but you could make the same case for scottish or welsch independence, or really, breaking political and economic power down into local communities. you might be able to achieve greater prosperity for some bit of time by consolidation, but then you are at the mercy of the powers constituted, and when things go wrong you are unable to do anything to shape your own destiny. that's why i'm a proud splittist. it's easy to picture the further consolidation of europe at this point as something that many people in many countries come deeply to regret in the long run: merely a way of generalizing the meltdown.