UcMiami it is precisely for the reasons that you list that I think Yale would be a good (if she wants it) move for Berube. She would not be pressured to win instantly and the Ivy playing field is relatively level. Princeton in on top now but Dartmouth won a few in a row in the early 2000's and Cornell, Penn and Harvard have won recently.
A move to an Ivy from Tufts is, as you say, almost a latteral move, but if she helped to re-shape the program there other opportunities (again if that is her goal) would open up. And there are worse places to be than on an Ivy campus.