What everyone is forgetting is that initially there were certain standards that were set for EU membership and for the monetary union.
The idea was that there would be stability and strength in numbers. The problem is that these standards or criteria were "relaxed" so that certain member states could join.
The likes of Greece, Spain, Portugal,and Ireland were allowed membership as they were deemed to be "On their way" to meeting the criteria even though they had not actually achieved many of the said standards.
Now that they are member states, their recovery is hampered by poor taxation collection systems and weak economies and have to be bailed out by the richer member states or China.
It's a simple matter of averages, strong member states offer stability but equally, if you have weak member states it makes it harder for the EU to recover as a whole, and that is purely from a financial view point.
Member of the EEC was about trading links (I think!) but membership of the EU was so much more.
I don't believe that we need to be a member of the EU to maintain trading links but I think that Germany and France would probably spit their dummies out should the UK leave.
Don't forget the EU wanted to put a taxation on financial transactions which would have meant we would be sending even more money East to support the weaker member states or to be wasted on EU bureaucracy.
As for the Euro, it's a no go area and is likely to be for the UK for many years to come.
But what do I know, I drive for a living!