Bringing back Devin Hester is a good idea because the Seahawks realize their chances are slim and they need to take whatever steps necessary to win their next playoff game. Entire careers and millions of dollars rest on winning or losing one game, so it makes perfect sense for them to bring back Hester at this time since he is available. Any other team would do the same and if they had not made this move, it would have been second-guessed for the entire off season if they lose.
Devin Hester has been a good returner, and if he doesn't have to take a lot of punishment, he should provide a boost for the Seahawks. He's struggled with injury lately and hasn't been eager to return punts, but maybe the playoff atmosphere will motivate him to do what he does well.
A team that does well is constantly reinventing itself. Tiger Woods at his highest peak always talked about how he was always trying to redefine his golf game. A team would never employ the same strategy at the last game as they employed at the first game. Bringing in Hester is a good way to try something new.
Devin Hester is one of the greatest kick returners of all time, but he is past his prime. He doesn't have the same big-play capability that he used to have. He probably won't make much of an impact for Seattle. Seattle will rely on Russell Wilson and its current offensive players to make an impact during the playoffs.