While it might be true that risk can be similar across many systems, the presence of dedicated players or factions changes the dynamic significantly. If my faction or I take an interest in a system, you can expect a noticeable difference in the level of activity and risk. Therefore, it's not entirely accurate to dismiss the idea that some systems are riskier depending on who's there.This is false.
Beyond a couple of 'popular systems' (which we can actually name off the top of our heads) there is no appreciable difference in risk between modes.
Cosmetics, like decals in COD&similar, are purchased for a variety of personal reasons. Self-expression, standing out visually, or simply for aesthetic pleasure. While some players may feel they're just for personal appreciation, marketing around these items often emphasizes customization, uniqueness, and sometimes even status among peers. So, while it might seem that they're only for personal enjoyment, there's a broader appeal tied to them, especially in multiplayer environments.Seeing others paintjobs/decals. In a busy instance you might get a flash of another Cmdrs paintjob, (or suit if they're on foot) you won't see their decals and certainly won't see their bobbleheads. The cosmetics are for your appreciation, and making pretty screenshots, nothing more.
If you're interesting in marketing around cosmetics topic I have reports with real data assessing how volume changes in single player/pve/multiplayer evninroments.