Put a large piece of artwork that you love on the mantel, leaning against the brick, and then add some accessories in similar colors and styles from there. You bring the colors into your dining room area to make the two areas work together. Odd numbers of things are always more interesting than even.

Photo collection wall? Or you could just place 1,2 or 3 canvas painting on mantle against wall.

Still got the pink chair?

HI -- If this was mine , I would not add anything more to it or on it --- I like it just as it is !

Minimalist.

I keep scrolling by this post and I really feel like overlaying tile on the brick is really going to update this fireplace. A large format 12x24 in a concrete look (available in many tones) or a subtle linear pattern is going to improve the look dramatically. From floor to ceiling; leaving the seated hearth alone.
I love the colorful slender vases pictured above on the mantel in the William Hefner architect picture plus one large painting to give it color and appeal. Less is more. As far as in the fireplace cubby itself, be consistent with some various sizes---one color. The mish-mash candlesticks don't fit the look.

You have enough candles and vases below. Consider layered pieces of artwork on the mantle, the largest piece hung on the wall and off center.
http://houzz.com/photos/2212268

http://houzz.com/photos/2821981

A clock as one above.

I'd keep it simple. Prop a painting up against the brick and boom, done. The painting I photoshopped in here is my Cheryl Danton Perkins. Colors were adjusted to mimic the lighting in your room.