Yurgir is your ally in final battle if you helped him and got rid of Raphael. He also has unfinished bussines with Raphael. Tav would recruit him basicly at the end of the game during act3.
I always thought about Roah as of somebody who should aid us in final battle if we were to helo her with Nine Fingers. Would be nice to have bard, but story wise having whiny halfling in your camp doesn't seem as interesting - I might be wrong about this, but all she could offer is jokes about her hight. Question is, would she join in act 2, or act 3 like Minsc, leaving no real time to get to know her.
I get Nere is second Drow, and yet another character with pointy ears. (most characters have pointy ears; half-orc, goblin, tiefling, even hags). But him being Drow male could lead to tension with Minthara. Which could lead to Minthara be even more mad at Tav. - Forcing Tav to a) manage them or b) get rid of one of them.
Him being quite naive and and easily manipulated with option to be told to not follow the Absolute makes it easy for Tav tosuggest him to join your crew. He also has inside knowledge about Moonrise Towers and from his desire to replace Balthazar we know he is quite ambitious.
And the game already acts as if saving Nere was truly important.
+ as I already mentioned, he is basicly already ready to go. His loot is two sword with dagger, necklase, ring, musical instrument, moonlantern, boots. His camp clothes could be the Absolute Outfit as who else would wear that hideous thing. And Robe of the Cult of the Absolute was already datamied, so it most likely should fit Tav if Tav chose to wear Nere's stuff.