As an adult reading this for the first time, I really had to shut off a good portion of my brain that concerns itself with 'plausibility' and 'child safety', etc. Once I did that I really had a jolly old time! On one level, the most important level really, this is fabulous escapist fiction for kids. Even now I found myself getting caught up in and deeply admiring Claudia's planning and execution of the big run-away adventure. On another level, this is about the little ways we find to escape the mundane and how we can feel special and unique when life seems so ordinary.
The 'feel' of the novel - the 1960s New York setting, the precocious heroine - are very like 'Harriet the Spy'. My daughter loved both equally, but is fairly devastated to learn that automats no longer exist.