While I understand the sentiment of wanting the very toughest and best conference in college football, I feel that some of the moves that are desired here would eventually lead to national irrelevance for the SEC. Destroying the Big XII, would lead to Texas dominance. Like others have stated, Texas does not need a conference to maintain its current revenue base. It does not need a conference to recruit. An independent Texas, or a Texas in a Big XII w/out OU and/or A&M, is a perennially undefeated Texas. An SEC with OU and A&M, is an SEC that would rarely produce an undefeated champion.
I think it is in the best interest of the SEC to push other conferences to be more competitive. The SEC should be pressuring the Big XII to fill the void created by Nebraska's absence with another decent football school (Iowa), should be pressuring Notre Dame to join the BigTen (if that is even possible, considering ND's independent revenue sources), and should be pressuring the non-BCS, competitive teams (Boise, Utah, etc.) to work their way into a BCS conference.
The best situation for the SEC would be to see every major conference with twelve teams and a championship game. Adding extra conference opponents, creates an extra conference game, and gets rid of either a bigger pay-off, nationally-relevant non-conference matchup during the season, or gets rid of an "automatic win" non-conference game. Neither of these, IMO, would be good for the SEC, if the SEC wants to continue to produce National Champions.