One of my sons actually learned to read from his Dad's Calvin & Hobbes bookes. It caused quite a laugh when "transmogrification" was one of his early sight words. Garfield comic books are their favorite French reading, which I will encourage for the same reason - they pour through them in ways they do not with their French readers.
I can't help a lot with looking deeply into C & H, because it is my DH who was reading adult level books at age 6-8 while I am much closer to average. DH knew that C & H would really capture their imaginations but I am not althogether sure he looked at it deeper himself. The down-side for my sons, was that they had Calvin's version of school fixed in their heads before they started school.
... If you do want to look more deeply into Calvin and Hobbes, how about the connection to the philosophers they were named after? Just a thought.
