These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Foreshadowing: The creation of Gaia/Galaxia is foreshadowed a couple of times.
On his death bed, Elijah advises Daneel to look at the big picture, which parallels Giskard's notion of the Zeroth Law.
In a conversation with Emperor Cleon regarding the emerging attempt to establish a legislative government for Trantor, Seldon expresses sympathy for the idea of democracy, but concedes that it is impractical for such a huge population as Trantor has (much less the entire Empire). Daneel (who among other things would serve as Cleon's first minister under the alias Eto Demerzel, and would act as a benefactor to Seldon) undertakes the creation of Gaia with the idea that if he could turn "humanity" into a concrete concept, and eliminate issues like social status, then it would be possible to make decisions about what benefits humanity as a whole without being limited by weighing individuals and groups relative values against each other.
Hilarious in Hindsight: ".... people had no real conception of the fact that the Empire was running down. They had been more or less running their own affairs since the Zeonian revolt..."
Narm: Hardin shouting "The Galactic Empire is dying!" No wonder one Encyclopedist called it a "hysterical" statement.
The original version is even more narmy, with Hardon declaring "If you ask me... The Galactic Empire is going to pot!" Asimov wisely changed this bit of dialogue to something more dignified.
Shaggy Dog Story: At the end of Foundation and Earth, it is revealed that the Foundation was nothing more than Daneel's backup plan, enacted during a time when he was having trouble setting up Gaia. Since Gaia is now operational and about to take over the galaxy, the Foundation and its history was ultimately irrelevant.