I think if your book is aimed at an audience whose electrical experience/knowledge is beginner-novice, having a reference to find parts described will ease the learning curve and many frustrations when it comes to building the circuits described.
If the aim is for an audience with a higher skill/knowledge level, then putting part references is probably irrelevant.
If the aim is for an audience with a higher skill/knowledge level, then putting part references is probably irrelevant.