With all that work to make it better, is there any chance of relocating the television? It's a bit high to watch comfortably from the seating you have and somewhat mars the appearance of the fireplace area.

The mantle is very attractive. Can you find another wall for the TV?

I agree with @houssaon that the current mantle is very nice as mantles go. Any chance you would just want to do the gas insert and call it a day?

You mention a gas insert. Are you talking about gas logs or an actual insert. Gas logs are much more attractive and don't require much for installation. An insert is a complete sealed unit that is more like a heater.

Anyways, we specialize in gas logs and glass burning fires along with all the screens and accoutrements to decorate a fireplace.

Here are some ideas:

Burnt Aspen Gas Logs with Custom Fireplace Screen and Andirons

Burning Glass with Geometric Shapes and Chrome Fireplace Glass Doors

Simple over-mantel to hide cords. Solid brass mini crown molding trim around opening in polished nickel with sliding mesh curtains. The fireplace trim matches the mantel. Burning black glass with geometric shapes. (this won't work...see below)

Edited: After posting this I realized that the last option is not feasible the way I created the mockup. I made it as if the wall was flat, when in fact this is a small wall that has some projection to it. This would work better if you can match the crown molding and just wrap it around the wall like this:

Just float out a false wall using 1 x 2s to hide your wires. Cover it with drywall and paint it the same as the rest of the walls. Wrap crown molding around the top. You may have to find building supplier that does custom millwork to match your existing molding if you cannot find it off the shelf.