I played around a little bit with the LensFlare.hlsl file some time ago and ended up removing the diffraction spikes altogether and thought it looked really good IMO to the point where i just replaced the usual sun texture (Star.dds) with a blank transparent one (not really viable beyond the asteroid belt region tho as it pretty much disappears altogether at that distance unlike the standard sun texture).
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One minor thing i'd like to point out tho for future reference is that the current lens flare implementation has this somewhat contrary effect on the stars as well as the celestial sphere background where they both seem to be considerably brighter when they're overlaid by any of the lens flare elements; but then again i'm completely ignorant on how this would actually behave in reality so it might just be a misconception on my behalf.