why not flick through a few trade magazines as they feature spas/salons.
also look online, you can even view salons on u tube.
glass cabinets with a light in are great and won't take up much room.
also floating shelves are good, you can get a set of 3 square ones from argos.
use glass beads, crystals, pebbles, shells etc to create more texture to your display. I've also seen feather boas with little fairy lights in them.
also don't have everything at one level, use small boxes or perspex shelves to create height.
i got 2 lovely white cubes which have batteries in and they change colour (and are completely cool), I don't often switch them on just using the size of them as part of the display.