The importance of the FIBA cups has been diminished to the point, where teams wont even participate in them anymore, because they would have to play without half their team.
In german Bundesliga, there are roughly 5 to 6 US guys on each team. Some have up to 8, thats the most I can think of and the most that are allowed, since teams have to have a certain amount of german players on their team.
The effect this might have, is certainly blown out of proportion by those, who favour stricter rules on non-EU players. Since more competition from the US came to europe, the euro national teams have gotten better than ever. Young prospects get to train with better talent and get playing time in minor leagues. Right now, the system is basically like in US baseball, with the exception, that you still train with your major league team and only play in the minor leagues. I think that has been proven to work well.