Although I am far for being a good Lisp programmer, I wouldn't recommend introducing Let Over Lambda (or anything about advanced macro programming) too early in anyone's learning curve.
For a comparable price (at least, when I bought them), Common Lisp Recipes might be a far better companion to PCL for an intermediate Common Lisp programmer.
Also see PAIP: https://github.com/norvig/paip-lisp
0: http://www.gigamonkeys.com/book/
1: https://letoverlambda.com/