As it stands, keeping the 'poorer' countries in the Eurozone seems like a very bad idea. The main reason being that -unlike the USA- people in e.g. The Netherlands don't feel a connection with people from Spain and vice versa. People in the northern European countries don't even feel a connection with people in the countries close to them, even though the cultures are much closer aligned (in terms of sobriety, work-ethos, etc…)

This I think is the main difference with the USA. The USA also has richer and poorer stats, but because of the shared language, history and culture, people in both the richer and the poorer states feel like a US citizen.