What OP suggested is similar to Euro, a single currency across boarder, and you see how much trouble it has now 
In fact, the Euro, as a currency, is behaving amazingly well. Those in trouble are STATES, not the money itself.
That's what I mean, you can't have countries with different political interest using the same monetary policy, an easy monetary policy will stimulate the hard working nation but crash the leisure seeking nation, but both a way of living and different view of life: In the long run we are all dead, some people will enjoy the life while others will work hard until they die