There is a lot I like about the book system. It makes books a valuable resource you have to search for, the drawback though is book reading is critical to skill building and it is about the most boring part of the game. I don't dislike it takes time, since time is a resource attached to zombie migration, hunger, boredom, etc. How I would change how books work would be to simply make it work similar to sleeping, just with a built in mechanic that would pull you out of the timelapse if a moodle became severe (i.e. you won't read if staving to death, very sick, having a panic attack, etc.) or a zombie was spotted or banging on your house somewhere. You could choose how long to read in hour increments and it would timelapse for you.
Another angle that could add more variety to skill progression would be to have static locations contain an XP bonus. For instance, a hardware store or a rural warehouse contain a special workbench and that is the only way to get a high carpentry XP bonus, Maybe an electronics store had a maintenance bench in the back for electronics. An automotive shop for leveling mechanics, shooting range for guns, etc. etc. The idea of having these XP bonuses would be that they would be worth the time to frequently visit, but given they are static locations scattered through out each town, it would require you to traverse the town to revisit them. Also to add more complexity, you are required to supply specific materials for each skill building task, electronics parts, wood, ammo, etc. this way you are driven to gather supplies to level these skills up, another reason to explore the map and loot more.