If you set it up right, it wouldn't devalue the regular season much at all. If you made it 16 teams with automatic bids to all 11 conference champions, the you have to either win your conference (regular season obviously is the ultimate decider in that) or you have to be one of the top 5 at large teams, which almost always will mean losing no more than 2 games.
Plus, if you set it up that way, you'd have teams from the MAC, Sun Belt, WAC, and CUSA in the tournament, which would place a whole lot of value on getting one of the top 4 seeds. Usually you couldn't lose more than 1 game at most and still get one of those freebie games.
Then if you mix in letting the first rounds be played at home sites of the top 8 seeds, you'd put even more emphasis on the regular season.
Let's take just last year as a hypothetical. If you played that scenario out, here is what you'd have in the bracket:
1 Auburn (SEC Champ)
16 Florida International (Sun Belt Champ)
8 Arkansas (at large)
9 Michigan State (at large)
4 Standford (at large)
13 Central Florida (CUSA Champ)
5 Wisconsin (Big 10 Champ)
12 Virginia Tech (ACC Champ)
2 Oregon (Pac 10 Champ)
15 Miami (OH) (MAC Champ)
7 Oklahoma (Big 12 Champ)
10 Boise State (WAC Champ)
3 TCU (MWC Champ)
14 Connecticut (Big East Champ)
6 Ohio State (at large)
11 LSU (at large)
Just in this bracket, Arkansas would've played their way into the bracket with their win over LSU. Alabama blowing the lead against Auburn knocked them out of the bracket. LSU cost themselves a first round host and possibly a match with UCF by losing to Arkansas. Boise cost themselves a home game and a shot at UCF with their loss to Nevada late in the season.
Had Auburn or Oregon lost a late season game, they may have fallen all the way to a match up with Virginia Tech in the opening round rather than FIU or Miami (OH).
Also, in this bracket, no at large team has more than 2 losses. Missouri, Oklahoma State, Nevada, and Alabama would be the 4 teams that finished just outside the last at large spot. Nebraska would've lost their chance with the Big 12 title loss. Just some thoughts. Obviously, you can take more losses and have an off day, but you can't take very many.
Ultimately, college football's regular season would have more games that mattered. The last weekend of the year, the only games that mattered were Auburn-SC and Oregon-Oregon State. No other game had any implications. The week before, the same thing with those two teams.