Your Mediterranean color palette is just looking a little stale. There are so many beautiful options for paint but I believe we should address the scale of your room first. Perhaps you can send a picture of your windows so I can suggest a treatment that would work with your wall unit. I would probably stay with a natural linen.....texture but no pattern.
With your painted wall units out of wood, I think I would stay away from additional wood product like "Shiplap". What I DO like about the Shiplap is the distressed texture which marries beautifully with a smooth painted unit. Therefore, if budget is not greatly restricted, nature stacked stone in tones of creams, golds and grays would be a dramatic addition on the fireplace stack.
I would add crown and a open display area on top of each unit with a crown. Inside of that display, I would add a large organic looking basket in each unit for additional interest.
It appears as if your units are 8ft. tall with 16 ft ceilings approximately. The additional height added to each unit will keep the fireplace stack feeling in better proportion to the bookcase units.
On the fireplace wall, a series of 3 mirrors line directly on top of each other would show a industrial undertone with its zinc frame and reclaimed molding. This would look very dramatic without it getting too busy.
Last, but certainly NOT least, give all your walls a wonderful chamois tone such as Ben Moore 1068 Squire Hill Buff
with a flat finish and a deeper camel tone Ben Moore 1070 Barley Harvest
in satin finish to the mantel and its surround. Put cream chenille pillows on your brown leather sofa and "voila"... You have a timeless, classic family room...you will never grow tired of no matter how long you have it!
Send pictures when you are finished ...we love seeing your creative juices flowing!
Have a Blue Sky day!