Well, i think your stuck in what i call limbo. Your not up to date on tech but not to old either. 1 thing i have noticed is your CPU, the AMD Athlon 64 X2 5600+ is a shocking cpu & i find single core cpu's better performing.
I would find the type of CPU you would like, Phenom II x4's are decent CPU's as i currently run from one myself. Then get the motherboard to suit. If your not into all this overclocking & benchmark bragging than any motherboard that has the option for upgrades of better cpu's & has USB3 & 2, sata II/III & 4 DDR3 slots for more expansion room should work well. HDD well, if you still have plenty of room then no point buying bigger. The GPU, if it handles the games you play well then why upgrade now when in the future...