No CS curriculum can ever both touch the whole spectrum of what there is to offer and be reasonable to mandate for all students. Inevitably, some students will want the minimum necessary for practical work and others will want to explore as many avenues as possible. The importance is in striking a good balance: exposing students to enough different paradigms to produce good computer scientists without requiring so much that they never get enough real experience with specific languages to be good programmers.
Using Common Lisp provides the option to do that, but there's still plenty from the realm of programming languages that would be left out. It might me a mistake to try to do too much at the high-school level though; C, Lisp and ML would allow access to a very broad range of programming concepts - far more than any three of the approved languages.
I don't think that it's an accident so many good programmers got started in BASIC then graduated to 6502 assembly. There's something powerful in that combination. We can go it one better with Python, followed by assembly on an emulated simple processor. Follow that with writing a simple compiler targeting the same processor. (In Python, perhaps.)
C is nice, but I've seen too many C programmers who really just think of the compiler as magic and have no idea what is happening there. To produce top-notch CS people, you should get as close to the machine as assembly.