In his commentary on Genesis 29:31, R' Samson Raphael Hirsch discusses the significance of Leah's status as less-beloved wife.
First, it's significant that the plurality of the tribes of Israel, including two that would come to be the most prominent - Levi and Yehuda - came not from the more beautiful, more beloved wife of Yaakov, but from her humbler sister. R' Hirsch doesn't say the following explicitly here, but this choice strikes me as fitting into a general pattern that the origins and leadership of the Jewish nation are almost never the obvious choice - the firstborn, the biggest, or the strongest. Examples of this pattern include Sheit, Sheim, all three Avot, the various leaders among Yaakov's sons, Moshe, and David. See also R' Hirsch on Genesis 17:17 (a personal favorite of mine;) where he talks about the joke that gave Yitzchak his name - incongruous success in extremely improbable conditions - being part of the essential message of the ongoing existence of the Jewish nation.
In addition, R' Hirsch talks about the exemplary way in which Leah overcame the adversity of her situation. She maintained her trust in God and worked, over time, to build a loving relationship between herself and Yaakov, based on her role as his children's mother. In his commentary on the following verses (32 - 35), R' Hirsch demonstrates how this building relationship is tracked in the names of Leah's first four sons:
Until Reuven, it was visible that Yaakov preferred Rachel.
Until Shim'on, Yaakov's preference was subtler, but still detectable by listening to him talk.
With Levi's arrival, Yaakov and Leah felt a strong marital attachment, like they owed everything to eat other. It's clear that this feeling was now mutual because Yaakov declared this name.
After that, having built a solid, loving marriage, Leah could enjoy her next son for his own sake, and burst out in thanks to God.
Thus, the difficulties of Leah and how she responded provide many archetypal lessons for the Jewish nation whose foundation she was building.