Aye, there are some I could split into layers! I've actually tried to come up with a reasonable way to approach this, and it would take a bit of time; the backgrounds have been made using multiple tools, and one of them would allow for me to split and export layers, while the other tool would not.. So I'll have to see what I can pull off!
In a few cases, some of these backgrounds can be layered really nicely using Additive Blending (The black areas will be transparent, and the nebulas will blend 'brighter' with one another) Though this is only useful if you are using an engine that allows for blend modes