I agree that you should change based on the personnel you have but Tubby basically has done what Croom has done and the square peg in round hold thing just doesn't work. Auburn's problems of late have been just like MSU - their QB's stink.
In the SEC it's near impossible to win big without at least a slightly above avg QB unless you dominate in other areas such as our defense in the last 90's.
Long term will Tubby's change work? Possibly if he recruits those types of players that make such a system work - and he is doing that. But how long will his patience hold and by the time he gets those players will defenses have caught up to the spread?
Most teams win with either superior talent, mediocre talent, but running something unorthodox that most teams don't run (ala Navy last year) or mediocre talent and superior coaching. More and more teams are running the spread so defenses see it more and thus it takes superior talent to run it - a lot of teams that have been long-time supporters of the spread are struggling more this year - like WV for instance. Their numbers aren't near what they used to be. FL's offense doesn't look as impressive, Louisville is struggling. Some teams still make it work quite well, but defenses are catching up a little.