Juventus has to be careful not to blow the wad on players that (while elite) do not fill a hole. Once the team has 11 top notch players, then they can go on shopping expeditions on nice prizes.
Offense is where the team has the most depth. Palladino and Giovinco are young, with a ton of potential, as well, Trezeguet and Iaquinta aren't exactly ancient. Not to mention Del Piero will be useful to some extent for the next couple years. A big purchase isn't needed here. Most I would do here if so compelled is go after someone young with a much smaller pricetag like Quagliarella or Huntelaar.
Midfield is a big priority area. Marchisio and Nocerino will be midfield stalwarts for many years to come. Marchionni, Salihamidzic, and Camoranesi have a few years too, so the right side is alright. Tiago, Zanetti, and Almiron are in their prime ages, so I'd say the centre is pretty set too. Left wing has serious issues. While Nedved is one of my all-time favorite players, he's just not the same anymore. Big money needs to be spent on an elite level LWM. Quaresma, Mancini, VDV, Vicente, or someone like that.
Defense is the other big priority area. Chiellini and Criscito will be stars... Chiellini arguably already is. Andrade is injury prone and there's no telling what he'll be like when he comes back. Legrottaglie is playing really solid right now, but that could change at any time. Boumsong is pretty much a bust. Grygera and Zebina are serviceable right backs. Jury is out on Molinaro, and loyal Juventino Birindelli is nearing the end. Major investment needed.
Goaltending is set. Buffon has many years at the top left. Mirante will do as a backup long term.
Long story short... while I'd love to see Aguero, he's just too pricey a luxury.
I wouldn't mind going after his teammate Ever Banega, or Diego Capel of U-20 Spain fame though.