Will you share a wider view of the entire fireplace wall and the decor around it?

If you rarely use it, I would store the spindly tools and the screen and put a large stack of white birch logs in the firebox to add some color and texture to the darkness.

We use blue as an accent color. Our living room and dining room are combined in an open room setting. In your opinion do you think painting the brick a little color would look good against the wood trim and floors?

What is your budget? Perhaps you can shop other parts of your house?

A chair and floor lamp would look great in the corner where the sideboard is now. For the other side, perhaps a tall floor vase with tall filler. It depends on what you have to the right of the cat house.

You don't need to spend a lot on money on "art" to make a space look decorated and complete. Large framed maps of places you like, mirrors, an arrangement of flat baskets, chunky shelves, etc. can all make a space look more finished. Just be sure to hang them at the right height and make sure they aren't too small and cluttery.

Use Romabio on the brick rather than paint, it allows the brick to breathe. Remove the dated mantle piece and replace with a new, clean line beam or a reclaimed wood piece depending on your style. Paint the vertical wood surround. Colors for the Romabio and wood paint should have some contrast.