First thing I would do is to upgrade to 8GB, which will also allow you to activate dual channel memory and get up to 15% better performance..
Second thing I would do would be to get a real 4 core CPU. Right now you have a 2 core with hyperthreading. You would be far better off with 4 cores without hyperthreading.
And I would do those in the next 6-8 months. Then start saving your money. A year from now, there will be a whole pile of new 16nm based video cards out there that will be much smaller, much faster, and for the same money as you would spend today.
Also, I see no mention of the heart of your system. The power supply.