I honestly don't want the playoff to expand past 4. I think it will devalue the regular season too much and that's what makes college football so awesome now. Every game counts.
I'd be OK with an 8-team playoff if it included automatic bids for the 5 major conference champions plus the highest ranked champion of a mid-major conference. That would reward conference champions and only have 2 at-large bids. Anything beyond that is too much. I'm fine with keeping it at 4 too, though (which is the way it's going to be for the next 12 years anyway).
I'll go further...I can't think of a year where more than 4 teams should've had a legit shot at the national title after all regular season and championship games had been played. That includes the Boise years.
College hoops is a great example. The regular season means nothing. Really no advantage to being a high seed.
But thats be because the higher seeds are usually the better teams. But there is really no advantage to being a 1 vs being a 6 or a 7. So the season means nothing.
The bowl games are just exhibitions outside of one game right now (three this year). How can you decrease the importance of games that mean nothing? The BCS is exactly what made all but one bowl game irrelevant to begin with. So what could a playoff do that hasn't already been done?