The answer to 'what was the surgery for' is simple for my family: Access. The surgery was to provide access to sound, which my daughter didn't have before.
But it seems right that the word "surgery" is derived from a greek word meaning "hand work." If we used that understanding, both of our quests to access sound and to access ASL would fit. 
I look at getting a CI and attending a school for the deaf in the same way for my daughter: both involve gaining access to language. Neither would have been part of her life if we had just let things be "naturally." Both routes provide access that didn't exist before and yet doesn't change who she is. Both paths were difficult, one required a one- (or in our case, two-) time significant surgical procedure and a continued reliance on technology. One requires a lifetime of change to how she learns, where we can live, what schools my daughter can attend, requires a 4 hour commute every day, and determines with whom and how she can communicate. Both have changed our lives to an equal degree, require her to work at developing language, and give her great pleasure in utilizing her access to sound and her access to sign.
I think the price is small compare to the immense rewards. In both cases.
