I love Kay and you should absolutely read any of his recommendations or at least examine them with earnest. That said, I struggle to remember anything he's created or written that's moved the needle (my needle). I'm honestly not hating and I have way too much respect for him to say anything on this list is not worthwhile. But, in my experience, Kay has been one of those brilliant uncles who's (written) work never see…
Ouch, why did I say anything. Feel like a hater :-/
EDIT: from a brief read of his wikipedia page:
"Kay has lectured extensively on the idea that the computer revolution is very new, and all of the good ideas have not been universally implemented."
Coming from someone with multiple major accomplishments (OOP pioneer, smalltalk, overlapping window GUI, etc.), that's a powerful message that can still be applied today.