I noticed a huge jump going from my old q9650 to i7-920 (x58 chipset). I also noticed a little difference going to z77x with the 3770k. The new cpu and chipset is more fun to play around with and easier to overclock.
The biggest improvement would have to be getting a ssd. That hdd biggest bottle neck in the whole system. ssd's are cheap now, I was glancing at the OCZ vertex 4 and its little less then 1$ per GB. Other wise I would recommend getting the Corsair force GT.