I think he is a pretty good buy for Juve - quality player, who comes at about the right price, considering he is almost 28 yo. He is not gonna take the team to a whole different level but I expect will prove to be very useful in Juve's bid for finishing in the top 3 next year.
The above takes into account that Vucinic would be used a SS or on the left of a 4-3-3 ... if he used as a LW in a 4-2-4, I just don't think he would cut it as he doesn't have the work rate or the physical build of a player, who would provide what'd be needed in that sort of position.
Like always, I'll have an open mind and give all new players the benefit of the doubt and welcome them to Juventus. But for 18M, I don't think Vucinic was worth it. Anyways, this seems more or less a done deal.