The problem with a '+1' model (as outlined and data compiled by Omnicarrier) is control of who gets in the 'semifinals'.
The Pac10 has already said they would walk away from the BCS if a +1 model was implemented:.
http://www.msnbc.msn.com/id/19985785/
and here's why. Most years - if just taking the 4 top BCS teams - you will have about 2/3rds of those teams coming from the SEC, Big10, and Big 12. However, if you only take the conference champions, you get a different set that is more favorable to the ACC, Pac10, and Big East.
Here is the data that shows the difference when Conference champions are used vs. just the Top 4 teams:
Going back all the way to 1998, if such a model were in effect then and forward:
Pac 10 teams 8 out of 10
SEC teams 8 out of 10
Big 10 teams 6 out of 10
Big 12 teams 6 out of 10
Big East teams 5 out of 10
ACC teams 5 out of 10
Utah once
Notre Dame once
Whereas if it had simply been the Top 4 BCS ranked teams, not limited to one conference representative in the semi-finals in a given year, this would have been the distribution:
Big 12 - 10 teams
SEC - 8 teams
Big 10 - 8 teams
Pac 10 - 6 teams
Big East - 4 teams
ACC - 4 teams
---> the Big 12, SEC, and Big 10 have 65% of the bids under a 'Top 4 BCS' scenerio.
No non-BCS representatives and no independents.