If you want to learn about symbolic AI, there are a lot of more recent sources than PAIP (you could try the first half of AI: A Modern Approach by Russel and Norvig), and this has been true for a while.
If you read PAIP today, the most likely reason is that you want a master class in Lisp programming and/or want to learn a lot of tricks for getting good performance out of complex programs (which used to be part of AI and is in many ways being outsourced to hardware today).
None of this is to say you shouldn't read PAIP. You absolutely should. It's awesome. But its role is different now.
If you read PAIP today, the most likely reason is that you want a master class in Lisp programming and/or want to learn a lot of tricks for getting good performance out of complex programs (which used to be part of AI and is in many ways being outsourced to hardware today).
None of this is to say you shouldn't read PAIP. You absolutely should. It's awesome. But its role is different now.