How about using it as a chalkboard wall? I like the idea of having the chalkboard framed on the wall so it looks more like a picture than just a whole wall of chaulkboard paint.

You have some true masonry work with beautiful brick. I love the little arches but your wall paint not so much from what I see on my screen. I think it would a shame and a pain to paint. Neither a thin white wash or a thick bright white on rhe bricks would brighten those rooms as much as repainting the walls. If the 3 other walls were lighter shades they would bounce more light on the bricks to make them appear lighter too. When I painted the wood stained wainscot in our breakfast nook to match our white trim, it brightened our windowless kitchen trenmendously. I understand you don't want to paint the walls, but that would brighten things more. Keeping the yellow in a lighter shade and the wainscot and trim in a warm white would work with the brick and your furnishing. I think a white shade from the brick throughout would unify and brighten the rooms. I could see covering all the brick in the mudroom with the beadboard like the wainscot and adding shelves and hooks. You could build a storage bench from stock cabinets. And paint it all the creamy color of your trimwork. I totally get the toy decor from the days when our kids were little. My sanity saver was a large wicker laundry basket to toss things in when wanted to enjoy a more grown up space after bedtime. Now that you dont need those gorgeous niches for wood, they are great toy storage space. A wood crate or metal wash tub could be more decorative hidden storage. (I have no stones to throw for plastic tubs. My baby has decorated our dining room with a couple filled with stuff going back to his dorm.) Also the brick will look lighter if the mantel is returned to a darker wood stain.

Are the walls painted a dark or bright, or deep color? If they are then i might think of painting them. If they are more neutral I would do as jmm said first. You can always give a painting allowance in the sales contract. The chance of YOU picking the the exact colors that I would are fairly slim. Wouldn't spend the money unless I had to

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