im refering only to to Unity Free here, seen the post processing effects with Pro and they look pretty fantastic.
Once your scene has been built, playtested, lightmapped etc, do you have any general tips for improving the look and feel of your scene? I kinda hit a stumbling block after ive lightmapped, and just start adding more detail but i feel like there is more i can do, although not sure what. Im talking in general terms here 
Can you show a few images of your scene?
im just talking in general terms
Are you going for realism? With a large poly and texture budget, it’s possible to spend an entire lifetime perfecting one large environment.
Make it be nighttime and turn it into a horror game, then you can get ultra realistic by having lots of black pixels. Just joking. Do you have any bumpmaps and other fancy shaders?
Ah yeh good ideas
^really?
Lightmapping helps a lot. That is often what I notice that is the tipping point between amateur-looking scene and moderate-looking scene.