You are asking what kind of running shoes to put on grandpa. They'll look good, fit fine and will work around the house. You can't expect just because they are running shoes, grandpa will sprint to the mailbox.
Adding even a low power gpu such as a r7 260 or gtx 750 to your pc will have the same results. The ddr2 for your board is more expensive for 1Gb, than for 4Gb of ddr3. Your processed is dated enough that it will assuredly suffer during more modern games, dragging down any performance from the gpu. Unfortunately, you are a victim of supply and demand, there being little demand for dated equipment, the prices get jacked high.
Honestly, a budget pc from Walmart or Costco will get you better performance, even with just integrated graphics. Sorry if that sounds blunt, but for what you'd spend in upgrades to revitalize your current pc, a Walmart cheapie would be cheaper.