I'm reversing the order of the posts because I think ORS answered the question before a700 brought it to light...
There are very few systems that have the MLB ready impact players a700 is talking about AND the talent to land players like Victor Martinz, Adrian Gonzalez and mid-season pickups. Generally, the systems that have both (say, Kansas City) come with a s***** Major League club.
Secondly, I don't put much weight into the number of MLB ready prospects when evaluating a system. If the Red Sox have, say, a future Jon Lester and Dustin Pedroia in their system, they shouldn't be dinged for not having the Reed Johnson's and Carlos Silvas at AAA, particularly when they have traded those guys away. Navarro, Hagadone, Price, Rizzo, etc., were all moved for MLB talent.
Is it worse to have a number of yearly all-star caliber players at lower levels than to have a number of role players at the top levels with few/none who possess extreme talent?
We have seen the types of elite prospects who come out of the system formed by Theo: Pedroia, Lester, Ellsbury, Papelbon, Bard, Kalish, etc., are all superstar caliber talents. Why is it worse to have a number of those guys in waiting than to have a few guys who are MLB role players waiting to come in now? I don't get it.
All those young guys at single A are not just average "good" prospects coming through the system. They are the product of two consecutive seasons where the Sox have stockpiled draft picks in the high rounds and spent loads of money to sign the guys they want. That's not insignificant. And the fact that there are not 3-4 of those prospects but more like 10-15 says that in a few years the Sox should have a very rih payout indeed. The farm system is not merely a place to provide backup/depth talent. If used correctly, it should produce centerpieces for the future of the franchise. We have seen them do that already, and I have no reason to think it can't happen again. In my opinion, even a guy as highly regarded as Will Middlebrooks represents the low end of the talent that should be coming out of the system in the next 3-5 years.
Roughly half of the Sox currently 40 man roster is home grown talent. That's pretty good and is what we should expect moving forward.