For the second, I don't see the point of putting sequins on it, since the fabric is shiny and shimmers in the light like satin.
Sparklies doesn't necessarily equal sequins. What I had in mind was tiny glue-on rhinestones or beads (although beads are probably too heavy).
In this case even just a thin light blue bias tape along the edge could help to enhance the visibility of the edge of the skirt. I once saw a black flouncy skirt with red bias tape along the whole edge (including red details in the rest of the costume) and this red bias tape really made all the difference to the costume.