Now, I know that we're actually comparing HSWT with TSNOTD and TMIAB, but Have Spacesuit wraps up with a potential doomsday scenario, and that made me think of Watchmen. I love that even in a YA book, Heinlein gets in the creepiness of "Their planet shall be rotated." A whole planet instantly separated from its sun - now that's scary.
Another similarity lay in the undeniable baseness and evil possible in humanity, and the need for some greater force (Ozymandius, the war crimes tribunal) to deal with the possible fallout of human choices. I love how clear my images of Iunio were, standing in the middle of some vast amphitheater, surrounded by aliens, in full Roman legionairre costume, and shouting "Witchcraft and making horns when the translation pipes in. So wonderful. I think that's something that was missing for me in Watchmen - the silliness and wonderfulness of people, even as they're awful.
Anyway . . . I need to NaNoWriMo. What are others wrap up thoughts in Heinlein?