I think "boring" is a key word here. If you genuinely want the outcome, doing the Next Actions is invigorating, not tedious... as a general rule, anyway. This has been my own experience, though I may be unusual in that regard.
You may want to reread those books but you may not want to sort the shelf. If you are find with having the books stacked up in no particular order, then there is no obligation to sort them at all.
Remember, GTD is about implementing the things that you want different so you can relax about them.