If you paint it to match the walls, do a satin paint. I'd prefer it match the trim and then paint the backs of the cabinets a darker shade of the wall color from the same color strip card. Or you can enhance the backs by using wallpaper over cut-to-fit luan that just slips in and removes when you want a change. Style the shelves with 1/3 books, 1/3 large decor items and 1/3 open space.

What are you expecting to get out of it? Do you want it to pop, or do you have interesting decorations or nice book covers you want to stand out instead? Painting it the same color as the wall won't look all that great I think, but that is just my opinion :) I have seen a few design shows where they used mirrors and bright colors inside the cubbies to make different things stand out.