I don’t think they’ll expand until the ACC GOR expires (nor do I really want them to for my own reasons) but I think you’re looking too short term.
FSU and Clemson consolidate and protect the brand. They are both top 20 home stadiums by capacity and would enhance the SEC product in all sports. They would be a threat to SEC hegemony in the South if they joined the Big Ten. No other school has the same impact.
UNC and UVA are about expanding the brand. They won’t be worth their payout but both have extremely high sports, including basketball (which is something the SEC is weak in), academics (ditto), and markets that the SEC has long desired. The SEC Network is headquartered in North Carolina.
The Big Ten can grab Miami or Georgia Tech but 2 Southern away games out of 20-24 won’t change their demographics. The rust belt is dying and the South is booming. Taking the two biggest targets of Big Ten expansion at forcing them to look West absolutely should be a high priority for the SEC.
If they can get the Big Ten to take Washington, Oregon, Stanford, Cal, Utah, Arizona State, Colorado and Notre Dame; that would be huge win for the SEC.
If the Big Ten takes UVA, UNC, Duke, Clemson, FSU, Miami, Notre Dame, and Stanford that can only be interpreted as a loss.