For those self-motivated learners, clearly you need to give them enough information to pique their curiosity enough to invest the time to study more outside of class. Give them too little and they will feel overwhelmed. Give them too much and they do not feel the challenge. Daniel H. Pink wrote about this in his book "Drive" (he refers to "Goldilocks tasks") which is about motivation (including motivating students though not limited to students). Clearly the "right amount" of information needed to pique one student's interest could well be more or less than that needed by another student.
That said, I think you are asking the wrong question. The goal must be to get the student to engage with the subject. Students already have so much information at there fingertips. The problem is not that they do not have access to the information, the problem is that they do not acquire the information. If they don't read the book or notes or watch the video or pay attention to your lectures, they will not get the information regardless of how much "food" you put on their spoon.
Today, the general consensus is that student engagement is key to learning and active learning is a powerful tool to improve student engagement. Active learning is not about how much information you give, it is about how you give them information (for example, discovery-based learning).
As one man said a long time ago "ya gotta wanna" meaning that one must have a true desire in order to excel. So, the issue is about motivation overall.
That said, one could ask a question, when students are engaged and asking questions about a task you have given them, how much should you answer directly and how much should you guide them to find their own answers? In this case, the discussion would move to quantity of information but it would seem that the answer to "what is the right amount" must be unique to each student or at the very least dependent on the quality of the group of students overall.
In the school where I teach I have different levels of students (different programs) and one group (weaker, less self-motivation) requires much more information to get them interested in solving problems. That is, I must get them 90% there before they will try much in the way of research. Other groups I only need to give them 20% there and they are happy to do the work to get the other 80%.
