I've heard it said that for now, the SEC is perfectly fine with what it has compared to the Big 10. Two very strong eight team divisions. Even if the Big 10 expands to 20 by adding four more PAC 10 (or 12) schools, I sincerely doubt that the SEC's bargaining position with networks would be impacted in any way.
And would splitting the pot 20 ways instead of 16 be worth it for the Big 10? Impossible to say for sure, but I doubt it. At that point, the Big 10 in a way would be bidding against itself. The two major money players are Fox and Disney. And the Big 10 is a lock to be one of the two major conferences. So why add four schools if it's not likely to lead to significantly more money? Notre Dame's the only game changer out there for the Big 10.