I rate it a bit below average because it's always CHANCE, and you know the rand, also it means that from the beginning you lack some important trait which may help your neighbour to outmatch you. Adaptive is definitely better, because it gives you some trait from the beginning. However it's better than no trait at all .
Honestly, why do you want it when you could have adaptive?
I noticed that one of the Balseraph's leaders had emergent in one of my games, and by turn 250, I think she had 5 traits plus emergent. That make sit way better than other traits. At most it should provide 2 extra.
Got ingenuity with the Doviello and still had emergent (iirc). That one was a big help.
It would be nice if the pedia entry would list which traits will remove emergent and which won't. Would help people stratagize which traits to make attempts for first without having to remember of the tops of their heads.
Now it sucks. Once you take a trait, you lose the emergent. So you get 1 trait to start with, and one more later in the game... which means you are like all the non emergent civs, except they have 2 traits throughout the entire game.