I'm not saying do "all" of our shopping there but working on that one superstar every couple of years would be nice. (Jovetic, Hamsik, Pjanic, etc all were brought for little )
First, there aren't that many superstars coming from these parts and second, hundreds of players from Eastern Europe do leave their homelands at very tender age, but few succeed at the top level.
It's hard to locate the player who'll succeed when he's only 15-16, and if you wait until he's 18, 19 or 20, he'll already be sold for a price we aren't ready to pay for potential (Modric, for example, was sold later than the other talents from Croatia, but that's why he was sold for some 20-25m euro).
Another thing is that lots of players whose surname ends with -ic and are doing very well nowdays, are actually born in some western or northern European country, and from there you're not buying as cheaply as if you would from the country they were born, or from the birth country of their parents.
Rakitic, Ibrahimovic, Pjanic etc were born or raised in west/north Europe.
Indeed, some Eastern European players like Hamsik, Vucinic etc were sold really young and for little money. Later they succeeded, but for every Hamsik who succeeded, there are at least 50 young kids who don't make it, and it's hard to find the one who'll succeed while these boys are so young.