On a pure gameplay level, I was wondering if more content was planned for the rooftops in the Lower City - as they have some detail and are well traversable - and the Missing Letters quest was intended to direct your attention to the roofs as possible areas of exploration. For the rest:
The quest feels very unfinished. In the Lower City Tara treats you like a stranger even if you play as Origin Gale; as Ametris recently pointed out, Gale has no real reaction if you harm Tara; there also are some unconnected chat lines about Gale's mom and his surname in the (romance ?) conversation with Gale after meeting Tara, when he invites you to Waterdeep. I agree that it would be nicer if you could invite Tara to camp after meeting her (maybe coax her with fish or boiled beholder eyestalks, as beholder jerky is her favourite dish) and have a longer camp scene during which she and Gale can properly reunite and you are given a deeper insight into the Dekarios family life.
A longer scene with Tara might also help explain Tara's catflap of displacement, a teleportation spell she invented, which gets mentioned in the epilogue, but I think is never spoken about in the game proper outside of Gale's Origin. As for the Origin, I would really like for Tara to return to camp after snacking on the pigeon's in because I dearly miss her in Act 3.
Tara as a summon in battle could be fun because she is an accomplished spellcaster and who doesn't love a fireball flinging tressym. ^^
