for a couple reasons, though i like lavezzi i dont believe hes the player to take us to the next level, as in be the difference between say finish 2nd and win the scudetto or make us more competitive for CL. Id prefer to spend the money on that kind of player.
Also, 30 is a significant landmark for a player, he might be worth 15 now, but in a year i believe that figure will be a lot less.