Can we get a picture looking towards the stairs from the kitchen? What kind of furniture will you be placing in front of the fireplace?

the best thing to do would be to drywall over both those niches, (leaving room for your electrical/cable box ) and centering that tv on the wall.

then I'd run a wood mantle (not that white one,,) all the across the entire face, basically something like this. you can have a neater piece of wood if you choose.

you could run a shelf below the mantle for books or decor too. the mantle could be any wood stain. I'd also paint this wall a darker accent color. And I get rid of that boring tile and do it with something else. I just stuck in some marble, but you could do any type of tile you like.

the peach tones of these walls really aren't helping anything look better. I do a dark charcoal or a deep blue gray or warmer gray on this wall. paint the air vents to match.

Here is pic with inspiration.

and my mocking up