JMO, I agree with the premise that milb is not intended to be a long time career but rather an apprenticeship. A majority of the players drafted in first 10 rounds each year are those that have been awarded a significant bonus to help them through what may be some lean years in milb and those that the organization prefer will someday become part of the ML staff.
Those that become career milb players and have become free agents get paid very well.
In many organizations AAA 40 man players are pulled up regularly to the club so that they can make extra money. AAA players are generally treated very well.
Remember the higher up you go the more you pay in dues.
For those that will become later signees, make sure that college becomes your first priority.