I agree with the "you don't sell the farm" argument.
but in honesty, how many of those guys never make it? probably a good %. I would be willing to give quite a bit from the farm for a PROVEN 40-50 HR guy. The odds are even the "safe bets" farm the farm system turn out to be good at best 50%. therefore, I would be willing to roll the dice on that... For example, estascio and scott.
you certainly don't trade a bunch of "can't miss" prospects. But you try to work a deal where you give a guy like astascio who has a good chance of being a productive player. and then package him with some guys that seem like they could be pretty good (scott, busholz, etc) but may not, and even if they are won't be all that special compared to a guy who can hit 40-50 hrs