While I didn't need a blow-by-blow description of Lucy's "problem" and her operation, we should bear in mind that Lucy and Jules were peripheral characters in the Johnny Fontaine storyline, and from the amount of space devoted to Johnny, we can infer that it was clearly Puzo's intention to have him as the second or third (after Vito and Mike) main character in the book.

I think Puzo intended to draw a parallel between the "illegitimate" business world of the Mafia, and the supposed legitimate business world of Hollywood, and the rise to power in each of their worlds by Michael and Johnny.

I always viewed Lucy and Jules and Nino and Ginny as simply added characters to help flesh out Johnny's story.

Actually, if you cut out the Johnny Fontaine story, it would be a pretty short book, wouldn't it?