I'm not sure there's actually another school out there that adds value to the Big Ten, that's a pretty high bar to clear at this point. Maybe Florida State and Miami as a package just because it gives you a huge chunk of the Florida market.
I do think the SEC can tinker around the edges a bit. Carolina and Virginia make a lot of sense for them.
My feeling is that it wont exactly be about adding value, per se, It will be about eliminating contracts, and pulling teams from the competition, and control, if and when it happens.
B1G (Fox, etc) and its media partners may want to take teams, in order to take them from or prevent ESPN or others from locking them up.
SEC (ESPN, Etc) and its media partners may want to lock certain teams in and keep them in their control.
B12 will want to add to its value, will want to shop to more partners or a better deal.
Media partners, may find value in eliminating a conference contract, while you may have to pay more to a couple schools, you dont have to bid on an entire conference. 2 schools at 100M is less than 16 schools at 30M, for Fox, 4 schools 100M is less than 16 at 30M, for ESPN, this is especially true when you are getting rid of the lower value schools. And then you have the B12 and partners, adding 4 schools at any price is going to be less than 16 schools for an entire conference.
Therefore moving into 2030+ it is beneficial for basically any media partner already in the game to eliminate another conference. Thus leaving the scraps to anyone like Amazon to bid on if they want to enter the field.
Yes there are other scenarios at play, but this is one of the ones I could see where it is not exactly about if a school "adds" value.