A few thoughts:
The bulk of the money made by conferences are the inventory of games sold for TV rights - the main being the tier one rights, such as Big Ten selling the marquee football and basketball. I believe Big Ten also sells secondary rights to Fox for non-marquee games. Then there's the fees made from MVPD's for carrying the Big Ten Network (BTN). For example, in states where there isn't a Big Ten school, the BTN is like a dime per subscriber. When Maryland joined the Big Ten, the BTN fee for MVPD's went from a dime to 75 cents as Maryland was now in Big Ten territory. That makes my belief adding programs with major state populations would generate a ton of subscribers.
To me, that would mean adding Syracuse and Virginia, home to two large population states that border the Big Ten's existing footprint. While adding a Texas or Georgia Tech could be interesting, that would be a paradigm shift for Big Ten culture as both are considered solidly in the south - generally not Big Ten territory.
Texas already has their own network, the Longhorn Network, and that is a point of contention between the Big 12 schools, as Texas basically runs the conference.
However, any ACC school would be tremendously difficult to poach because of the recent Grant of Rights extension. The payment for leaving the ACC would far exceed anything the Big Ten is offering in order to join. The Grant of Rights doesn't expire until 2036.