How much would it be worth to (name your interested acquirer) to have immediate access to hundreds of millions of viewers daily or weekly? How much would it be worth to not let your direct competitor have that same access?
Getting more granular, Yahoo! may be the only major company that has partnerships with all of the following: Apple (AAPL), Google (GOOG), Microsoft (MSFT) and Facebook (FB). Pretty good! The total market cap for those companies is, very roughly, one trillion dollars. All of them must constantly be updating what they would pay in a bidding war for Yahoo!.
Then there are other major contenders. Yahoo! is a media company. Why wouldn't Comcast (CMCSA) or Viacom (VIA) and their ilk love to have those eyeballs? Even Disney (DIS).
Given an enterprise value of perhaps only a couple of billion dollars, my guess is that the real enterprise value of this company to an acquirer is much more than that. I need to leave guesses as to how much more to others who are more conversant with the appropriate metrics, though.