Let me spray my college tuition hypothesis on everyone.
My opinion is that college tuition is driven by the desire and ability of the very top colleges to spend money on students.
Example
Harvard has a gazillion dollars and can afford not to charge tuition if it wanted to, but it doesn't because people will shell out bucks to go to Harvard because it's Harvard. Harvard has so much money they can pay their staff whatever they want, they can fund whatever studies they want and they can get the best equipment and labs and facilties and still not have to worry about anything from a financial standpoint. In the endless race to be #1 and "keep up with the Joneses" other colleges have to spend similar amounts of money and do similar things just to stay highly ranked. It's a spending war, so to speak. Schools don't cover costs on ever increasing tuition not because educating a student is fundamentally that much more expensive, but keeping pace with the Elite schools and what they are doing and trying to position yourself as one of the best schools in the country/world is very expensive.
Soooooo......unless there is some fundamental shift in how college institutions and educations are percieved then regardless of endowment, tuition will likely never go away......maybe if the elite schools did it others would follow, but something tells me that probably won't happen.