Yes a more modern graphics card will help. The shadow maps and high resolution textures do make the card work harder. But I don't suggest buying one now as it is still quite a long time until release. We cannot give any estimate. I hope to be able to add graphics options to make it run better on older cards but maybe we can see about that when it gets to test patch stage.
NOTE: I'm just thinking out loud, these thoughts are how I imagine things going, not how it will actually happen, and they are not promises.