Whether or not built-in bookshelves add value to your home depends on how you build them. Rather than building static shelves, install a system that allows the shelves to be moved and the configuration changed. This gives future homeowners the ability to use the shelves the way they want to. Build your shelves from quality materials, and be sure to do a quality installation. You may be an avid DIYer, but it may be worth the added cost to have a professional contractor do the installation for you. The final consideration is whether or not the shelves look like they belong in the room. A family room may benefit from built-in bookshelves, but the kitchen may not be the right place for them. If you do your homework and create versatile as well as attractive bookshelves, then they can add value to your home.