Team spirit was one of the intangibles Rafa Benitez didn't have much time for
But then you look how important it is to managers like Mourinho and Ferguson - two men whose success is largely based on creating a 'them against us' mentality amongst their squads
I don't think it has a great amount to do with the nationality of players in the squad
spot on. the benefits of tean spirit only show themselves in adversity as in theory the whole squad pulls together and are seen as one. This can occur in two ways either collectively ie poor decisions and whole team is affected(Arsenal fail here) or individually when a player is not playing (ie adebayor spits his dummy out). A strong team spirit will reduce or even eradicate the negative effects these situations have on the squad.
As mentioned Rafa's biggest failing was not to succesfully harness a stromg team spirit. The Alonso saga probably cost him his job as players ceased to understand the logic behind it.