My objections to the single currency, therefore, are historical and cultural, rather than economic. I have read Mundell. I understand the benefits of a single currency, where there is economic convergence.

I think that's an incorrect interpretation of Mundell.  If memory serves (haven't read it in years), the cultural and historical elements, at least to a degree, are implicit in Mundell's view.  They're important to issues like labor mobility, similarity of business cycles, risk-sharing, etc.

Be nice to America. Or we'll bring democracy to your country.