The European Union is just that, a union of European countries. Those countries that qualify because of boundaries should be allowed to apply for membership. If they are willing to abide by the guidelines of the Union, then they should be allowed full membership. However, if any country which applies is engaging in activities contrary to the by-laws of the Union, they should be first be given a warning before they are excluded, then if they refuse to abide by the Unions laws and rules, they should be excluded with option to apply at such time as they come into compliance with the EU.
A lot of the instability in the EU was caused by allowing irresponsible nations into the union, like Greece and Portugal. Letting in even more small countries with bad economies will hurt the strong countries like Germany and France. The EU should not get any bigger. In fact, it should probably get rid of some of it's members.