I can almost control the density in full neb mode.
I hope no one else has figured out how and that I have your attention.
We don't do it through coding, well not much anyway. We do it in artwork. I was playing with an idea for a system (tan poofs coupled with a skybox), and I stumbled onto it.
I took purple poof 2, and lowered the opacity to 30%. Saved it as PoofTan01. I also lowered the opacity on an nback and saved it as nbacktrans. Had fantastic results, could see the skybox really well, but you were flying through dust clouds. The problem is, we can only have 6 poofs to choose from.
I propose a slight bit of coding. Instead of choosing between the six poofs listed on the neb table via check boxes, we remove the 6 poof limit, and we remove the check boxes, instead we have 6 drop menus that we can choose from. These drop menus would pull the information directly from the nebula table, and list all poofs found as well as <none>.
Then we turn around and put out a whole slew of poofs at different opacity levels, say 12.5% increments per color. Like PoofBlue01-12, PoofBlue01-25, PoofBlue01-37, PoofBlue01-50, etc etc to 100. We do this for each current poof as well as new colored poofs. We do the same with nback, and remove the 10 nback limit.
The only problem is this:

What can we do about it? If we can figure this one out, we are good to go, and can control nebula density.