draft and follow...In my opinion, would be geared towards the player drafted in the lower rounds because the scout feels there is a problem with signability or that the kid should go to school for a year and add a year of maturity to his body and to his game. The organization maintains rights to the player until a week or so (not sure the exact time in days...could be a few days instead of a week) before the next June draft. Gives a club nearly a year to work out a deal with the kid.
Signing with a 4 year school would not necessarily improve your chances of being drafted in a higher round, if only because the teams might simply stay away from you if they were unwilling to give you a bonus and also provide you with "coverage" for school tuition as part of the bonus package.
I would say that signing with a 4 year school gives you leverage to get more money but I wouldn't say that it improves your chances of being drafted in a higher round. If you are already likely to be drafted in a higher round (top 5 rounds), signing with a 4 year school would make very little difference to a team. They budget for each round, likely including an amount for college.