Frank, your "realpolitik" approach with a 10 ton bulldozer is a recipe for... war. You may think it's a game, but if you follow Russian politics and media, they're itching for a fight, and I can understand them. It's this imperial logic of "your back yard and our back yard" as you point out, that sets nations on collision courses and creates the basis for violent conflicts.
The Serbs got along with the Albanians in Kosovo for hundreds of years - there were ups and downs, sure, but in general, the two populations managed to find common ground. As they did with the Bosnian Muslims and the Croats - in general. What's been happening in the Balkans over the past 20 years is largely the result of foreign imperial efforts to extend one's back yard at the expense of the other's.
You point to a real problem when you say: "the only nations that have clout in the EU are..." which is precisely the reason why Serbia's politicians aren't interested in joining the EU; they don't want to be just another banana republic in Germany's sphere of influence.
The second major problem, as Jérôme correctly points out, is making decisions impacting international law outside the UNSC.
What baffles me and disappoints me is that our continental EU politicians just can't seem to wrench themselves from Washington's and London's destabilizing policies. From missile defense to Kosovo, the Anglo-objective is to drive a wedge between Russia and continental EU... A number of reasons are behind this: ensuring that NATO continues to have a purpose and stays in Europe, keeping an energy rich and geographically imposing Russia at bay, and I would even add - contributing to instability in Europe itself, given that the real danger is in a rock solid EURO which is becoming the world's reserve currency of choice.
So, what I would expect from out dear leaders in Paris, Berlin and Brussels is to (in this order):

1. Stick to international law and the UNSC
   
2. Get an independent foreign policy which is in the interest of Continental europe
   
3. Build constructive relations with Russia