One little quick fix would be to spray paint the gold a black color. Probably need to use paint intended for hi heat.

Remove the clutter and paint the walls a fresh neutral. Don't sweat things you cannot change. List the house and see what happens. It may be easier to give the buyer a credit if they ask for one.

When we purchased this house last year, everyone knew that the house needed painted because you could see bare spots down to the aluminum siding and peeling paint. Since it was the dead of winter and entirely too cold for the previous owners to paint the house, we got them to come down $5,000.00 on the price of the house. We are paying painters to paint my house for under $4,000.00!

Personally, I think the marble fireplace is gorgeous!! It is worth far more to leave it as it is, and you will absolutely ruin its value if you do something horrific like tiling over it. If you are getting ready to sell the house, the marble fireplaces should be featured as a selling point. They add to the value of your home.