I think that his key component in his game, aside from the fact that he is a 12-13 goal scorer whilst not always playing in his preferred position, is #1) His vision #2) the fact that he doesn't have a weak foot.
What his vision and anticipation does, is that it forces the opposition to draw to him, and not just in one-on-one coverage either. It forces defenses to shift to him. If you look at the past couple of seasons, you'll notice that what he does, when he draws such opposition to him, is that he is able to quickly and more often than not correctly place the ball to a teammate in a position where that teammates chances to score are exponentially higher.
The 2nd point of him not having a weak left foot is not just solely relegated to his ability to score with both feet. It has much more to do with the fact that because of this, he is a nightmare to gameplan for. You can't, as an opposing coach, just say to your squad "Keep jovetic to his left, and he will be negated". Doesn't work that way. His ability to use both of his feet on both sides of the pitch, on the ability to turn towards goal and place an accurate shot using either foot, is instrumental.
And as far as the complaint that he doesn't score enough goals to warrant that price, think about this for a second.
This Juve model is not based on the individual, but on a combination of players working in unison, with cutting, running, anticipation, and a variety of players scoring goals. Let's keep in mind that players such as Vidal and Marchisio don't score goals solely on the premise that no one else can, but it's because the have that ability,along with Pogba to be able to score goals from the midfield position. This squad is not based solely on the individual, but the team. This is where the impact of a Jovetic, in my opinion, will be felt the most.