I'm in almost the exact same boat, not much to upgrade there: Socket 775 and DDR2 are obsolete so the only sensible upgrade path for CPU/RAM is a complete platform upgrade. The PSU is the only part listed worth carrying over and if you are on a budget, you could also reuse your video card for the time being.
I have a C2D-E8200, 8GB RAM and I'm thinking about upgrading to i5-3470 with 16GB RAM. I plan to reuse both my Radeon 5770 which is still more than sufficient for what little gaming I do and my 650W EarthWatt PSU. I haven't decided between reusing my Antec 300 case (I like my cases as gimmick-free as possible) or getting something newer with USB3 front ports. Since the 5770 is the only add-in board in my current PC, I might go mini-tower/mATX.