1. I live in DFW and I can tell you that TCU has had an enormous amount of support from DFW this year. You couldn't turn on the news or drive down the street this season without seeing it. Nobody was talking about t.u. (admittedly down) or A&M (surprisingly up), it was all Horned Frogs. Despite my protests to BCS bashing coworkers about there being a problem if your signature wins for the season were Utah and Oregon State, there are about a million homers over here. The problem is that was for this past season, a second straight BCS season. Their success is not sustainable and a marriage to the SEC would only precipitate that decline. For every bump they get in recruiting by being in a conference with national credibility, they'd lose it in eligibility issues to retain Tier 1 status. They'd either be middle of the pack or the Vandy of the West. Also, they're hot here, in DFW. Unless you're an alum, you're not going to be paying attention outside the metroplex. And we already have the SEC Network on Channel 21 here. Oh, and TCU has about 9,000 students at any given time.
2. A&M's footprint is much larger than Houston. You're thinking in terms of proximity, but there are as many A&M grads in DFW as the Houston area. (DFW is a bigger metro area than Houston, by the way.) All you have to do is look for grown men wearing their ridiculous class rings (cling to the past much?). In fact, adding A&M would give the SEC a foothold in DFW (6.3m), Houston (5.7m), San Antonio (2m), Austin (1.6m), El Paso (742k), and McAllen (726k). Even 'tiny' Corpus Christi rivals Jackson in terms of population. Those areas alone give the SEC access to about 17 million people, just by adding A&M. You're right, they can be dorks whose traditions borderline on the ridiculous, but they're an army and are spread throughout a population of 25 million.