I think the UK is not representative of most EU nations in that it does have that strong global finance position and a strong currency which possibly makes it more viable to go it alone than many of the EU nations would find it
Sterling has fallen in value against the euro since 1999, sterling is not what it was, previous to that, i recall a series of devaluations in the 60s and 70s (before EEC)
As far as i can see, per capita, we are around 23rd richest country in the world, not even top 10 in europe, in absolute terms, on par with France/Italy, way behind Germany.
But as i said earlier, together we are lot stronger than our individual parts... or rather we were.