People don't feel what they don't understand even if this is touching because they don't catch it, that's in the real life and sometimes it's frustrating. Anyway back to the thread...
For Sara is interesting because like McHale said "I like make things ambiguos because in that way people can interpret it in many ways", this is the case in the extra content For Sara.
For Sara it's really the tape that Wirt make for her and it's act like sequel to the events in the series. Wirt express how much he loves The Unknow and his people and how he suits better in that place, he talks about his dead father (who seems to be the real reason behind his interest in the poetry).
An interesting point about For Sara is that Wirt talks about a girl, but he never name her and anytime that he tried to said her name he is interrupted
"My dear... my dear... my dear"
That's because McHale wants keep it ambiguos but it seems like he is talking about Beatrice (weird I know) because he mentions constantly Birds, "In the morning we can fly", a guide, a feather being separated of it's bird, and a girl who is shy about her feelings for him, and it ended with him asking himself if Beatrice will remember him now that they were separated.
A poem in a particular taks about this girl, it's called "Me, frozen" this title seems to be a reference to episode 8 when he is rescued from the frozen lake. Wirt says "I open my eyes and I see... like the melancholic voice of my father, like the kiss of my first verse, [he metions god but I don't remember this part]...boy... I think that I'm in love..." When was rescued the first thing that he looks is Beatrice and he basically compares this person with many beautiful things.