Hmm, well it's hard to say. Your game choices are pretty modest and don't need so much power. You could add to your current build, something like a $300 upgrade to the get 8gb ram, a graphics card like the r9 270 and a 120gb solid state drive.
(would need to know your power supply)
All of those parts I listed you could actually be reused in a new computer again if you wanted to build new later on.
If you were interested in building new, you could do something like these. I assumed you didn't need an operating system and had one.
*not sure why, but rebates aren't being applied*
Both builds are around $610 after rebates.
Amd Build 8320
http://pcpartpicker.com/p/bBm4Bm
Intel Build i5-4440
http://pcpartpicker.com/p/PGfJmG
If you think you might be into overclocking or SLI/Crossfire, the AMD build will be better for you. I put in a nice power supply that's on sale and would be all you'd need for a long time and could handle any single card you wanted along with a few dual cards. (7 year warranty/gold rated to
)
If you aren't into that kind of stuff, the intel build will be the way to go. I put in a h97 motherboard so you can upgrade to one of the new intel CPUs in a year or 2 if you wanted to.
Other than that, the rest of the parts are the same on both builds. Do your research, you will find many intel vs amd topics turning into huge wars about which is better. There will probably be some of that in this topic to sooner or later