Keep Vidal.
Just look at Liverpool, who has the guy in question, Suarez, right now. Great attack, average midfield/defence = no trophies
We are the opposite. Great defence/midfield, average attack = win
What I said about Liverpool can be said about a dozen other clubs in Europe; that they have a great attack, but are lacking in the midfield and defensive departments. Atl. Madrid and Napoli are other good examples.
We have proven, and we're on our way of proving for the 2nd season in a row, that it's much more important to have a great defence and a great midfield if you want to win. We look likely to retain the scudetto, we've beaten the likes of Chelsea in the CL and absolutely slaughtered Celtic. All with an "average" attack, but a great midfield and defence.
Ideally we'd be great in all areas, but if we can't, I'd rather keep things the way they are.