Sunday it is

[H2Finally]

I think the space is too small for a focal point. Visitors will be looking straight to the living room beyond. Therefore, just a smallish plant (exisiting plant too eye-cathing), some painting (instead of mirror), and maybe a small light colored area rug to provide texture (instead of clashing with the light tile floor).

Instead of painting the walls, you may consider painting the trims darker. Changing the carpet to hardwood would be perfect to 'anchor' the black railing.

For instant gratification, hang some small, dark / vibrant colored prints/photos on the walls along the stairway; and maybe a series of small potted orchids on the ledge at the middle landing.

Other than that, my suggestion is next time you're taking a photo with a mirror in it, put on a pair of pants..