Vsync can act in different ways. If I am playing a game that will run consistently above 60fps, the enabling Vsync saves the work that the GPU is doing in rendering those extra frames, and it will run at a steady 60fps.
If I am running a game that will drop below 45fps, Vsync can be a bummer, as it will often (though not always) automatically drop to a steady 30fps even though without Vsync, the title might never drop to 30fps. I can feel the difference when this happens, and it is distracting, even through the FPS remains playable.
CPU limitations are pretty static. While a GPU limitation can be resolved by lower graphics settings in an attempt to keep solid framerates, a CPU that can't run decent FPS simply won't be able to do better without overclocking or upgrading.
As for how much of a limitation the CPU can incur, that depends completely on the title being played. The heavier the dependence on the CPU, the more it will be limited by a slower CPU (GTAIV, Prototype, Dirt 2 for just a few examples).
If you were to buy a 212+, and learn to OC safely, you can find out for yourself if your CPU is overly limiting. This is a pretty low risk purchase, as you don't lose the investment should you find your current CPU incapable of meeting your expectations. If you are willing to invest in a new mobo+cpu to resolve this issue anyway, the it can't hurt to try save some cash, unless your time is too valuable to take on learning to overclock (not an unreasonable situation).