It's interesting how you use the word 'tangible' because anyone can see passes, crosses, tackles, dribbles and shots, and judge a player based on those. Like the Parma game for example. He did those things, so we can say without any ambiguity that he had a good game. He had a free game. We were at home and it was a 4-1 result, could have been 7-1.
Away from home at Siena, we kept a clean sheet, gave them no real chances, yet he's still playing in a two man central midfield with a player who offers next to nothing defensively. I said in my match notes that he struggled in one on one situations, that he didn't want to make any tackles and just jockeyed his man. He also didn't commit himself too far forward. He didn't make those surging runs into the box. That's not because he forgot how to do it or couldn't be bothered, it's the set up of the team. The midfield from a tactical point of view was successful as it protected the defense for most of the game, that includes Marchisio not leaving Pirlo isolated and facing dribblers, and also a strong contribution from Pepe and lesser so Giaccherini. It also had sufficient attacking opportunities to create chances, just that Pepe and Giaccherini spurned most of them in kind. Ideally we'd have a player who can do both, but there is no Nedved or Camoranesi available to us. That game suited this approach. It also has to be said that Siena are have scoring problems.
I'd be quite surprised if the Bologna game is similar, they will probably have three CM's and break when they can, so in that respect it might be better to have the cut and thrust of Vidal and more offensively biased wide men. But Marchisio has also shown that he is not limited in this respect. I also want to see Vidal play a protective role at some point, a role he has played for other teams before.