Those games have been out a long time, so I'm not sure you would even need the extra RAM for them. Back when Left 4 Dead 2 first came out, I ran the game on a system with only 1.5 GB of RAM, a single-core processor, and a graphics card somewhere around the performance level of that GT 710. And I originally ran CS:Source on 1GB of RAM and a slower graphics card than that. That was running WinXP though, and 7 will require more RAM for the OS, but I suspect your existing 4GB should be enough for those older games. Any games requiring more RAM than that would probably also require a more powerful CPU and GPU anyway.
I wouldn't expect any demanding recent games to be playable on the system, but older games like that might run well enough. The CPU will likely be more of a limiting factor than anything. Looking at information about it, it likely has lower per-core performance than that single-core processor I ran those games on, but double the cores, so performance might be faster in some titles and slower in others, depending on how they utilize the second core.
If your power supply were capable, a faster graphics card might allow you to increase your resolution and graphics settings, at the very least. A GT 710 is quite low-end by today's standards, and might be fine enough to run the games you listed at around 720p, but will likely struggle at any higher resolutions than that. A faster card might be preferred, though your CPU will undoubtedly limit frame rates.