Any reference style book that is deemed good by your community is always worth reading at least once. It will do a few things for you, reinforce what you know, correct ideas that you think you know, and possibly teach you new things all together.
For this reason I generally suggest to every programmer that I know to get involved with doing technical reviews for the various book companies that have such openings. I generally do a lot of book reviews for Manning but have also done them for O'Riely too. I am sure you can get connected with Wrox, APress, etc.
The key here is several things. You get free books as they come out rather than when they are released to the book store. For me this means that you get to know about new technologies before others do (such as ASP.NET MVC, Hadoop, Lucene, etc....deep understandings in the cases where there are no previous books). You generally also get a free copy of the book once it is released. For those with egos (I don't know of any such programmers :P) you also get your name in the book. Lastly, some companies may pay you for your review efforts as well.