Hey Main Sequence,
thanks for your quick message.
I have exactly the same lines on my graphic configuration file (regarding Environment, Galaxybackground and planets) and what I saw is an increase in the starfield + core background. It looks brighter, with more stars and sharper (more defined I mean). I'll post a screenshot later on so that you can check.
I hope I didn't hallucinate (you never know).
For the planets, I didn't see any difference at all. Unfortunately.
Yeah, it seems they maxed the planet textures after horizons released. So it won't make any difference any more, but background should work.