Gregg Doyel has presented some interesting perspectives as to how the major conferences are actually the biggest proponents of expanding the NCAA Tournament from 65 teams to around 80 (the column also goes into separate conflicts over non-conference guarantee games). The rationale here is that the major conferences would be the most likely beneficiaries of additional at-large slots. Illini head coach Bruce Weber says, "[I]t's not a surprise that the big guys are clamoring." The high mid-majors that have been receiving multiple bids recently such as the Missouri Valley Conference and CAA are also for it (albeit with a little less enthusiasm), but the smallest conferences don't believe they would benefit from an expansion at all.
For the record, even with my admitted major conference bias as a Big Ten guy, I'm completely against expanding the tournament to this level. In my opinion, the tournament should only be expanded to a maximum of 68 teams, where there would be 4 play-in games involving the 8 lowest seeds playing for the right to a matchup against each of the number one seeds. Anything more than that would severely dilute the prestige of the event overall.
Plus, the largest knock against college basketball is that it has the least important regular season of the major sports. At least with the current tournament format, the last month of the regular season provides a ton of excitement in weeding out the teams that are on the bubble. Expanding the tournament to around 80 teams would pretty much allow every team that would have been on the bubble in present times into the dance. That might add a couple more days of tournament interest for those who don't start paying attention to college basketball until March, but it would come at the expense of eliminating what is now the most valuable and entertaining aspect of the regular season. As a monster college basketball fan, that's definitely not worth it to me.