1) Every shira in the Tanach is associated with a miracle: shiras ha'yam commemorates the splitting of the sea, the shira of the be'er celebrates the water from the well of Miriam, shiras Devorah commemorates the victory over Sisra, etc.
What is the miracle associated with Shir haShirim?
Chasam Sofer in his derashos answers that it's a shira celebrating the fact that after all we as a nation have been through, we still sing to G-d -- it's a shira celebrating shira itself.
2) In the Dayeinu song we mention that "ilu... lo he'eviranu b'socho be'charava - dayeinu."
What exactly would have been accomplished had G-d split the sea but not brought us to the other side and saved us? What kind of outcome would that have been?
Netziv explains that the key word is "be'charava." Of course G-d would have split the sea and brought us across to save us from our enemies. We assume there is hashgacha pratis on the Jewish people. But who says G-d had to do it in such a way that you didn't get mud on your shoes? Who says he had to transform the riverbed into dry land to make it easier for you to walk on?
What this line of dayenu is telling us is that Hashems' hashgacha does not just extend to the preservation of Klal Yisrael's existence -- it extends down to the little creature comfort details as well.