I just finished reading this. Great book and I agree with your analysis. While the central conceit of the book and many of the arguments were already known to me, Spooner made one particular observation that now seems so obvious that I feel daft for not having already considered it.

"If any particular act is simply a vice, then a man who entices another to commit it, is simply an accomplice in the vice. He evidently commits no crime, because the accomplice can certainly commit no greater offence than the principal."

Followed up with:

"This principle, that to the willing no injury is done, has no limit, except in the case of frauds, or of people persons not possessed of reasonable discretion for judging in the particular case."

This idea, that the accomplice can commit no greater offence than the principal, is 180 degrees from how the war on drugs is fought by the state. And this practice is so universal, that until I read this book I had never considered the absurdity of it.