Well, first of all, much of the SEC is not toothless hillbillies, and people who kept saying that on HF were not sticking to facts. UGa, UFla, Vanderbilt, A&M--these schools are without a doubt "in our league" academically, and Nashville, Baton Rouge, Athens, GA, Columbia SC, Knoxville TN, even Fayetteville, AR--these are easily "in our league" as college towns. I have heard that the trip to UMiss is a good one, but I have not been. Also, I haven't been to Gainesville, but I bet it's a nice college town. So, the first point is that the myth that the whole southeast of the US is an ugly place with stupid people--well, that's a pretty ridiculous prejudice. All the girls on the sidelines of Alabama, Florida, Georgia, South Carolina--they all had teeth.
I think the SEC was cheating all this time, but now that coming up with money for the players is legal, well, we should be able to do that just as well.
Plus, we have to acknowledge that A&M being in the SEC is/has given them an advantage, and has given the whole SEC an entree into Texas for recruiting. You listed 1999 as a time-frame; at that point, we had in addition to UT and OU, A&M, plus Nebraska (multiple hx of national championships) Colorado (won a NC), Arkansas (same). Our strength of schedule has fallen while the SEC has gone up.
So, some of it isn't "upside" but avoiding further downside, where we may go 12-1 and win our conference and not make the playoffs. Also, even in years we go 9-4, we could have huge sellout stadiums with name-brand SEC schools coming to town.
In the same type of year, we might not be selling tickets to KSU, ISU, etc. Even when we are having an off year, I would be excited to go see UGeorgia in Memorial Stadium--10x more than seeing OkState or Baylor. That is, my season tickets would be worth a lot more to me. And, Georgia may not be that much harder to actually beat than TCU or Baylor or OSU, but the amount of credit you would get is far more.
There are a lot of HS players in Florida, Alabama and Louisiana that would love to go out of the deep south for college (to Austin), and would do so if our schedule was filled with the names of schools familiar to them. So, we could benefit not only with Texas recruitment, but across the South. So, I see lots of upside.