Yeah, I guess the idea of Spock having an older half brother that rejected Vulcan teachings wasn't too bad. I did really hate the way they used Sybok in the movie, and having him be Spock's half-brother just seemed like a cheap twist just for the sake of having a twist, and not something that enhanced the movie or Spock's character.
I completely disagree the contrast is almost poetic. Now I wouldn't be so surprised if indeed Sybok does turn up... just cause we haven't heard that he's there yet doesn't mean he isn't. Given the apparent awareness of detail those involved have concerning Trek and all.