The only position on a team that shouldn't always be subject to competition is QB after you have a solid starter. Competition in QBs breeds controversy and flip flopping the position has such a negative ripple effect on the whole team.
Every other position is fair game, including running back and stars like freddie. I love freddie, but I hope he realizes spillers role is going to vastly increase.. as it should. If by chance we make it to the playoffs, freddie will be better off for having spiller take a big load anyways.