A single3 currency for anhy region is lubnacy. Has the European debacle taught you nothing?
A single currency for disparate ecoomies is suicide.
Take Greece for instance. Normally its currency would devalue, exports would become cheaper,(devalue) and it wwouuld trade its way out of its debt. However, with the value of the currency mainly linkeed to France and Germany, this option is not available.
How could, for instance, Nauru, have a common value currency as australia?