What everyone is missing: the biggest advantage of the Euro is debt. Once you can take loans out in Euro, investors can give you lower rates since they’re not worried about a national bank going haywire and debasing the local currency. Also no potentially illiquid currency markets that need to be cleared going in and out of the currency.
Ask a homeowner the difference between a 2% loan (euro price) and 5% (local currency) and you’ll understand why so many countries have opted for the Euro.