Nice work!

I do think this image is more realistic than the first one. I think you're right in saying there's not enough light in the scene to show up much.

I haven't done much 3d compositing like this but I've done a bit of 2d work. Little things like the direction of the shadows (a difference of 10 degrees will stand out) or the position of a highlight in comparison to other things in the scene determine whether an image is real. In compositing 2d images even getting the quality of the light to match for the two images is important in making the final image believable. Many people wouldn't be able to tell you what's wrong with a scene but their experience of the real world will let them understand intuitively when there are mistakes.

Of course if you are creating an art work this is of lesser importance and you use what you need to produce your final effect. However, you did say you wanted to achieve realism, and I think that's much harder.