I agree with Lars "bigbraader" in almost everything he said (I just don't use texture AA). It seems we have similar ways of looking at things, interesting.

3Desktops, IMO the lighting is much more important than the render settings. I think that's in the lighting settings that you should focus more intensively. In the render settings, I think you should basically try to achieve a good trade-off between quality and speed. Your render settings are not optimized for speed, at all.

For example, in the vast majority of cases you don't need texture anti-aliasing. You're just wasting CPU cycles with that. Texture AA is typically necessary when you see Moire patterns (visual interference caused by repetitive patterns). Otherwise, don't use it. In all my images, I only used it once.

The advanced effects settings are way too high. You only need it that high if you see, for example, noise in procedural terrains, light leaks from radiosity, and some other circumstances. I typically use around 42%.

Regarding lighting, there's no "right" setting for the sky dome gain. It all depends on your scene. For example, if you have a high light balance, you probably need higher sky dome gain. In your case above, you have a low light balance, so you should probably have also a lower sky dome gain than 2, unless your sun is very low in the horizon (in this case you might need more than 2). You really have to understand what each thing does, and that's by experimenting.

You must also play with your materials. If you increase the sky dome gain, you're increasing the ambient component in your materials. Some materials are more sensitive to that than others. For example, the fabulous grass pack from Bigbraader has some cases where the materials have a sum of diffuse and ambient components higher than 100%. If you use a high sky dome gain, this grass could look washed out. You may need to decrease the ambient component of the material. I do that a lot. Almost all bigbraader grass that you see in my renders is adjusted to the specific light conditions of my scene.

Tip: You should tick the "indirect skylighting" checkbox in the radiosity section.