I like the light trail that you get from having a Sun Flask equiped.
It would be nice to add that effect to other weapons. Or similar flashy effects, or make your sword look it's flaming, or like a SoS or greensteel to impress the gullible. Add the bright pink of chaos. All sorts of stuff.
Something like the cosmetic helmets would be good, as they can be reused, unlike the cosmetic armour.