I would just paint the mantle white and see what happens when you put new paint color on the walls.

I agree with dclostboy about painting the mantle white.

The woodwork on the windows is lovely, and the existing curtains & rods hide that. I'd probably find a curtain or blind option that doesn't hide all the great woodwork trim.

I like when things "match", and from the pictures you posted it appears that one side of the fireplace is not the same width as the other, unless it's the angle of the picture. If that's the case it's not possible to do matching window seat/storage/shelving solutions on each side, which is what I'd probably do with the space.

The photo angles are a bit off. Both sides of the fireplace are symmetrical. I, too, thought of doing some small built ins on either side but am afraid that the tall (long) windows will prohibit this.

The mantle top is a real cheap piece of plywood (box) that is painted an odd dark gray. I like the idea of painting it white but am afraid that there just would be no contrast. Thoughts on painting the brick black or another color and the mantle white?

Also, does anyone have thoughts on the types of sconces to replace those that are there? Maybe a small ORB with white or linen shade?

black would be great. either way, you need to beef up that mantle. Cover part of the brick detail below.

As far as sconces, there are zillions. We need to know your style.

I really like Candace Olson sconces

http://www.aflighting.com/candice_olson/product.aspx?panel=0&category=Sconces&title=Sconces%20&%20Vanity%20Bars

If you're going for authenticity, these deco ones might work, but I love almost anything from Candace. Feeling like a little whimsey? These bottle ones are fun.