Those are some of the advantages that online interactions have over face to face interactions, although I disagree with a couple of the ones you listed which I'll get to shortly. However, face to face interactions also have advantages that online interactions do not have. Face to face interactions allow instant feedback. When I post something on Slashdot or a similar forum, at the very least I have to wait a few minutes for a response and often times I have to wait longer or I simply don't get a response back at all. This instant feedback leads to an overall flow of back and forth conversation which is also an advantage that face to face interactions have over online interactions.
One of the advantages that you listed for online interactions is that it is easier and more convenient to interact with those of similar intelligence levels. I would argue that unless a person is uncommonly gifted, they should not have trouble finding people who are their intellectual equals in a college environment. At a larger university that has thousands of students, I also don't see how time would be that much of an advantage. My university has 50,000 students and I can go on campus at any time of the day or night and find people who are studying or otherwise involved in academic work.
Again though, I would like to reiterate that I do not think online interactions are worthless or even less valuable than face to face interactions. I simply think they are different and each one is valuable for different reasons. And in relation to my original post, I think face to face interactions as well as other reasons justify the existence of colleges and universities.