Lord Ellpus
You raise a lot of issues that are very real, and that is one of the reasons I am so impressed by the EU. Just imagine what balancing acts it takes to coordinate all those countries that have different political, economic, taxation, social, religious, etc., systems, and you can have the biggest headaches for those EU bureaucrats, not to day the government of each EU country that has to comply with all the stringent EU requirements. I am totally, but totally fascinated by all this!!
I think it is a good thing, not only for the EU countries, but for the rest of the world, to have a stronger and bigger EU. Certainly, "free trading zones" help improve the economies of scale and exchange of goods and people, within the zone itself, but trade should be secondary to security issues and social peace (i.e. not lead to social upheavals). The EU has worked so hard in the past to achieve what they have achieved, and we would not want to see those efforts being wasted by the entrance of countries (whichever those countries may be) that would de-harmonize the union.
As for Turkey being Muslim, I think that that may not be such a big issue. I read an article in a French magazine that said that - surprise, surprise! - in France, there is a huge population who is Muslim (the 2nd ranking religion in France), so huge that the French were getting alarmed and worried. I think there are some other EU countries like that too (maybe Germany?).
As for the euro, one thing for sure is that it makes it easier for North Americans to exchange currencies if they want to visit Europe.

But I can see the problems that you mentioned, and sympathize with the individual countries.
By the way, there is a nice link that "defines" what means Europe. Take a look, for fun.
http://encyclopedia.laborlawtalk.com/Europe