I agree. He doesn't stand out in Empoli, like Giovinco does... and if he was as good as we all hoped he was, he would. (Granted I've only seen three Empoli games this year, but its enough to establish a pattern) Someone compared Marchisio to Brighi and that might be a good analogy. Serie A excellent, but not Juventus excellent. He'd be a solid starting midfielder on a team like Udinese, but on a full strength Juventus (as will be the case in a year or two), he'd be a reserve player. I don't think he'd be better than fourth choice on the currently wounded Juve team and we're all expecting (and probably receiving) midfield reinforcements in the coming year. (After Zanetti, Tiago and Nocerino in my estimation).
May as well swap him and some cash for a guy like Zapata who will definitely be a contributor for years to come.