"paint removable foam board and place it in the back of the bookcase, giving the look of a painted bookshelf, but without the commitment." Even easier...foamboard comes in colors. As long as you can find a color you like, it's as simple as cutting it to fit each shelf. You could even have each shelf be a different color.
DIY chandelier. Spray paint a bare branch white, make it a perch for clip on songbirds. place removable adhesive hooks on ceiling, then hang the branch above your table using jute or lace/burlap fabric scraps. Tie hanging tea lights or votive holders from branch w fishing line. Light votives (or use LED candles) and watch it sparkle!