I think it depends on what look you're going for. Personally, I like the rock face, but think the framing looks dopey. But you could drywall the whole thing and go super modern. I would suggest you look at fireplace photos on houzz and start an ideabook with the ones that inspire you. See three totally different styles below:

I would lighten the mortar. Then I would add some large pieces of art on either side of the Fp and hang or use a larger mirror over the mantle.

This has been a popular project lately. Mine was similar to yours in that it went all the way to the ceiling. I covered it up with drywall. It would be easy for you to do it because yours is already framed with the wood.

I would remove the wood that's framing the fireplace and put in a new mantle that is larger and more in proportion to the rest of the fireplace - Maybe 18" high. I don't know if the mortor can be changed but it could be lighter - maybe a tone darker than the stone. One very simple thing would be to spray paint the brass fixtures on the doors to black. Built-in bookcases from floor to ceiling with attractive molding, matching the mantle, would be nice but that might break the bank. Good luck.