Listening to Corey try at length to explain "mythic significance" in the context of Magrathea and the garden that may or may not have fairies at the bottom—it seems to me that most of the examples he gave kept feeling circular or tautological. It's significant because it's mythic. There's something more than what's on the surface, i.e. it's significant.
I think there's a more obvious way to describe such things as an island in the middle of the ocean where you love the view and might want to build a summer home but which may or may not be Atlantis: it's that there's a story associated with it. There's a narrative. By visiting a place with a story, you're experiencing that story for yourself; and usually, by doing so you're inserting yourself into that story and becoming a part of the narrative yourself. People who come to the story later will inevitably hear about you.
So even if Zaphod isn't inherently "getting" the mythic significance of Magrathea in the sense of caring about how big a deal it was historically, he's seeing himself as Indiana Jones, the star of a story in which Magrathea's myth continues to matter in that the story of its rediscovery is itself a mythic narrative.
I think there's a more obvious way to describe such things as an island in the middle of the ocean where you love the view and might want to build a summer home but which may or may not be Atlantis: it's that there's a story associated with it. There's a narrative. By visiting a place with a story, you're experiencing that story for yourself; and usually, by doing so you're inserting yourself into that story and becoming a part of the narrative yourself. People who come to the story later will inevitably hear about you.
So even if Zaphod isn't inherently "getting" the mythic significance of Magrathea in the sense of caring about how big a deal it was historically, he's seeing himself as Indiana Jones, the star of a story in which Magrathea's myth continues to matter in that the story of its rediscovery is itself a mythic narrative.