It's not really the level of exchange that's important in addressing the question of whether the euro is a failure. The issue is whether it's done what it was supposed to do, which is envigorate the European economy. It did not. In fact, it appears to be holding the European economy back. The reason it did not work is that in order to assure that the money supply grew at a homogenious rate, they established a long list of regulations, covering everything from what a member nation could charge in taxes, to the amount of debt they could incur, etc. Those kinds of regulations are not only impossible to enforce, but even if they were enforceable, they would end up killing local economic initiative, leading to slow or negative economic growth. That's what they've got now.
It's also hard to get the economy going when everyone is a socialist. Kind of reminds me of the days before UPS when I would go to the post office. There would be a long line with one person working at the window and four people doing absolutely nothing but shooting the bull. The guy doing all the window work was rude and in no rush. If you didn't like it you could drive your letter to wherever it was going. No competition ...no worries. It must be hell living in Paris.