Jovetic not scoring enough goals is a concern as long as we dont have a prolific (+20 league goals/season) finisher in our team.
We have plenty of forwards than can work as support strikers, being usefull upfront one way or the other. But the main concern is a goal scorer.
So this is why our investment should focus at getting a great tool for our greatest weakness.
Investing a major ammount to upgrade from Vucinic/Giovinco to Jovetic would be extremely unwise considering that we have not the complementary tool we need the most.
Jovetic is great at creating chances and all, but he needs a player at his level able to convert them.
After we acquire a player like Higuain, or Tevez, it would make perfect sense to sell one of Vucinic or Giovinco and upgrade him with Jovetic.