12 teams and negotiated a deal with Fox/ESPN and allowed them to create the PAC-12 Networks. The TV revenue for that first year of the new contract was $175M and the PAC Networks paid them an additional $82M according to their tax filling for 2012-13. They went from $85M to $252M in total TV revenue, one year to the next, by adding two schools.
The Big 12's new contract pays them as if they had 12 members. Adding two additional members will not give them any more TV revenue.
Your points are all valid but the Big 12 doesn't deem them that important. That's why, at the national AD's conference, Oliver Luck said:
"there are no "available teams" -- schools from the non-Power Five leagues -- that would add value to the Big 12's per-school revenue."
I think our window of opportunity was in 2011. A new one may open but it will be many years from now IMO.
http://espn.go.com/college-football/story/_/id/11066269/big-12-ads-say-no-discussions-expansion