I think iwen's right that the mentoring system is a good mechanism for preparing the team for life after the current coach - so probably a better system to have in the second term rather than the first (and every coach deserves a second term unless they are a halfwit ;)). I think in the first term, if the coach wants to put his own mark on the team, its a good reason not to have the system.
That said, I'd be interested to see how the system would work over a longer period of time. I put the full blown mentoring system in place in my last season as coach (partially to prepare the team for the new coach, and partially because I just didn't have the time anymore). That would mean that this season's crop are the 18yos that got put through that system. I expect the fact that we have a decent team this season is more down to iwen's hard work than the system, but it would be an interesting study ;)