The benefit to getting a CUDA-capable card would be that AE CS6's raytraced 3D actually becomes usable. If you find that you would use these new capabilities for real production, by all means get a new card, but you won't benefit from a better card in any other parts of AE than the raytraced 3D rendering.
I use 3D layers a lot, and sometimes lights. The CUDA would not benefit that?
I know it's not related, but would there be benefits using Maya?
After Effects' OpenGL usage is pretty minimal. The card you've got likely does the same job as a newer card for general AE work. As Jonas said, where you'll really see a difference is using ray traced rendering in AE, if that's of any value to you.
Re: Maya, yes, it will be beneficial to have better GPU in Maya.