Like Brett said the FX 4100 is not bottlenecking your graphics card.
The FX 4100 is actaually a pretty decent CPU and the graphics card is what's bottlenecking you.
I suggest overclocking both your CPU and graphics card and you should see a reasonable increase in FPS.
Depending on what games specifically you are playing and at what resolution and detail settings, the FX-4100 can and will indeed bottleneck a GTX 570, although the bottleneck in question is usually not that substantial in the majority of games on the market.
As far as the processor, yes, I would just wait for Steamroller before actually upgrading the CPU itself. PileDriver is worth looking at in the form of FX-8350s or 8320s, but I just don't see the point in such a gainful improvement.
Now you say your processor "definitely" bottlenecks you on Planetside 2, I googled for results, I couldn't find any specific benchmarks with that processor, I did however find this article, if you haven't tried these things, its worth a shot since they're "Free". Are you playing it in DX11 mode? The Bulldozer CPUs tend to fair somewhat decent in DX11 vs older DX9 for some odd reason.
I would definitely wait for the next year for the Steamroller.
For a time being get an SSD your system will be a lot better with SSD rather then your "green" hard drive! Even the cheapest OCZ will make a huge difference compared to your HDD.
That would be worthwhile. Green hard drives tend to be slower, as they're geared more for mass storage with lower power consumption. SSDs beat traditional harddrives green or otherwise in both speed and power usage (then again, hard drives really don't use much power to begin with).
I would suggest at least 128GB, ideally 256GB, technically you could use a 60GB but between Windows7, Virtual memory, and NTFS formatting, you'll use almost 20GB of it. Since a single game can easily take over 10GB nowadays, you can see how that creates an issue of space.
Its the other way around with RAM and storage, the hard drive reserves space as "Virtual memory". The amount of virtual memory is dynamic, you can manually set the parameters, generally you want at least 1/4 of your system's RAM, in your case this would be 4GB. With 16GB, you probably shouldn't need that much.
Back in the times of WinXP RAM was more expensive than hard drive space, RAM is obviously faster than virtual memory via a hard drive, I might be wrong, but if storage space is a concern, I don't think you'd take a performance hit if you were to limit your paging file size to something really low like 500mb.