One thing I'm not sure about it the scheduling element. In a 12 team league you are forced to play an unbalanced schedule in that no teams will have the directly comparable conference schedules. It would be their 5 divisional mates and a few other from the other side (which would vary by school) and then the non-conference schedule.
In a 16 team superconference, you could theoretically have much more comparability in the conference schedule. Each team plays 7 games in its own division, maybe one annual "rival" game with the other division and then the non-conference schedule. I'm not sure this is a real benefit but it is definitely a difference.
Last thing is the concept of economies of scale for the conference. Just like in business, the larger you are, there are benefits in terms of perceived and actual value. For instance, a B1G Network that passes 70 million homes instead of one that passes 40 million homes is not only worth more on an absolute basis (since it has more eyeballs) but is likely more valuable even on a per team basis since a larger network that is more national in scope attracts more interest from advertisers, etc. The key is that the additions that are made need to be accretive to the existing members (even though there is one more mouth to feed, they end up contributing more to the whole than they take).