Well, the issue becomes after 16 you start getting diminishing returns because you start losing TV windows big enough to pay for your adds. The B12 adding Pac teams, as pointed out by someone a few pages ago, allows ESPN/Fox to get some late games by adding a few teams, than having to pay for them all.
If you can't get Oregon or Washington, its not because they want to stay in the Pac, its because they want to wait for the B1G. In that case, take Arizona, stick at 14, and wait 5 years. They want something bigger than where they are or what you offer, so its just a terminal case for the Pac. Once they leave there isn't a big risk the remainder can rise from the dead. The B12 bounced back because there were fringe properties to sustain them.
Outside maybe Stanford for ND, who is coming for Cal, ASU, Utah, OSU, or WSU? Or, who can those schools add to rival you? Boise? SDSU? Tulane? Nerp.
Those 3 remaining seats in the B12 are now very valuable and the Buffs said why: Stable (even if its just stable because no one else but people at band camp will date you), media deal with ESPN/Fox, and exposure in three time zones, including Texas and Florida.
The hardest decision right now is for Oregon and Washington. No way the B12 allows them to temp it and, unlike the Pac's agreement, the B12 has a $100m buyout. So do you hold, hoping the B1G takes the schools on the West Coast that USC/UCLA don't want them to bring, or do you give up your dream to become the big kids on the new block?
Oh, and if you wait too long, ASU/Utah may pull a Colorado and steal 15/16 as they wait for you to cheat on them.