The reason the basketball season is somewhat devalued is not because there's a playoff; it's because there are 64 teams in that playoff. Every halfway decent team gets in. It would be easy to set up a playoff system that kept the intensity of the regular season intact -- you just eliminate or severely limit the number of at-large teams. An eight-team playoff, with six conference champions and two at-large teams, would be all right. With only two at-large teams from all of college football, every game would still be critical. You could go ahead and pencil in Ohio State or Michigan for one of those slots every year, because their conference sucks, but that's another matter.
One problem with that scenario is the conference championship games. For example, if that framework had been in place last year, LSU would have been pretty happy not to have to play in the SECCG. They would have been almost guaranteed of getting in the tournament, whereas the loser of UF-Arkansas wouldn't have made it. You'd have to figure out something to do about that. But in theory, an eight-team playoff would certainly keep the every-game-is-critical intensity that we have now.