Well DX11 isn't going to magically give you better graphics, if you were to take DX11 and covert this shader we have now it will very likely still look exactly the same the problem lies in the shader it self, it's not a particular complex or good shader.
The biggest issue is the light mapping, it's really bad, if you were to update that to a reasonable standard coupled with different light source types especially point and spot lights, and Volumetric lighting or any type of light scattering, you will be amazed at how much better the end results will be.
That said DX11 while it won't improve graphics on it's own, I am more interested in the performance enhancements that comes with it with regards to rendering.
You would need a new shader in order to make use of displacement and AO, but you still need a better lightmapping system to make use of it effectively which when don't have.
Win7 pro, Intel 2500K @3.7ghz 660GTX 8gig ram 16tb HDD