The following assumes you want a gaming system. If you want something else (video edit for example) say so.
Net: All you need is good video.
i56-2320 -- Great processor, no need to upgrade for a long time. 95W max tdp.
10 GB mem -- 4 is minimum, 10 is plenty. no need to upgrade.
nvidia gt 520 (or even worse integrated graphics) -- REALLY WEAK for gaming. This needs upgrade.
sound - fine
wireless - fine
disk - 2TB 7200. fine. SSD for faster boot if you want it. Raid 0 for speed if you want it, raid 1 for data protection if you want it. But current disk is fine for gaming.
power supply -- 300W