So sorry I haven't enough time to participate on weekends. Let me just make some brief points - hopefully you can confirm, expand, internalize these on your own.

*) A sky dome is not going to light your scene. You cannot expect the figure to look different by adding a sky dome, except for reflections. The Diffuse and Specular nodes do not look at the environment, even though they should. In other packages, such behavior is called Global Illumination model, or in olden days Radiosity. Poser doesn't have it.

*) Nevertheless, my original point stands. Your should not light your dome! The dome "glows" on its own. You should be able to see the sky even from a scene rendered with no lights. That's what I meant about plugging the sky color (and clouds usually) into the alt-diffuse channel.

*) If you are willing to do the following work, it is worth it. After you have designed a properly glowing sky dome and ground texture, you want to prepare a custom image for IBL that matches the environment. If your central figure is going to be close to any large objects, like a wall, they should be included too. Now I won't go into too much detail, but here's what you do. Put a sphere right where the figure will be. Make it super super tiny. Make your render size square, usually around 500 pixels. Switch to the "Front" camera and adjust dials until the tiny tiny ball exactly fills the preview window. Put a perfect mirror shader on the ball. Turn off all your lights except an IBL, which has BLACK in it to start. Render the scene. This first render, all you should see is glowing sky in the ball. Save the render. Attach it to your IBL - this is your IBL image now. Try setting the IBL strength to somewhere between 50% and 75%. Now render again. The ground is now lit by the sky (and other objects too) and will show up in the mirror ball. Save this render as your new IBL image. Render again, save as IBL image, render again, save as IBL image. Eventually, the amount of light may converge on WHITE or BLACK. If so, lower or raise your IBL strength as appropriate. If it converges on nice mid level tones - you've succeeded in creating a custom IBL image for your scene. You can then continue on as normal.

*) You cannot shade 3d space - I'd sure love to - except using the Atmosphere shader, and that is hard to use and slow and applies everywhere.

*) You can shade multiple cloud layers (domes) - I've never done that very well, but last time I tried I was not so good at shaders as now. I may try again. I can see it being reasonable to light cloud layers with diffuse and specular.

*) A single dome shader can have glowing sky and lit clouds combined. You just do the sky color part without a Diffuse node, and do the cloud part with a Diffuse node. Combining them will look cool and be much easier to give to other people for sky dome work by noobs.

*) This high-resolution business is a waste of time. The no-Diffuse part of the shader gets to decide the color of every single point  - it doesn't matter what the geometry is - more polys doesn't change the shading rate. The parameter Min Shading Rate changes that.

*) The Diffuse/Specular part of the shader will be improved by more polys up to a point. However, I think a sphere around 600 polys has achieved 99% of the realism that a 60,000 poly sphere would. Remember that we're really dealing with the difference between the normal on a true sphere, versus the normal on a piece-wise linear approximation of a sphere. Once you have about 30 segments around a circle, the error is very small from the linear approximation. Do not be fooled by the PREVIEW!!! That is not doing per-pixel shading with an interpolated normal. It is doing per-VERTEX shading with an interpolated specular value! This is extremely different (and way way faster) and should not in any way cause a reaction in you as the render will not be using that technique at all. More polys will make the PREVIEW better because, just as you predicted Ay, as you get closer to one-poly equals one-pixel the results look like per-Pixel shading, even though it is per-Vertex preview shading. But who cares about preview?

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)