I think they´d be better off expanding their best studios ( a third EAD Tokyo Team, a handheld/ second Team for Retro etc.) and collaborating more with third partys than buying a big publisher.
Far too risky and expensive.
Edit: What they are doing now....but more of it !
And don´t bother with Square Enix. Eidos´ studios are in shambles and so is the japanese branch....save for a few gems here and there.