While everyone agrees SP is important, one has to wonder exactly how important.
In 2002, in a meaningless final game of the season, Tim Wakefield gave up 2 hits in the 6th inning, and both runners scored (one as an inherited runner with Bobby Howery on the mound). Those 2 runs raised Wakefield's seaon ERA from 2.70 to 2.81, pushing him behind Barry Zito (2.75) for 4th place in the AL.
Had Wakefield simply come out after 5 innings, the Red Sox would have had the starters who finished first (Pedro Martinez - 2.26), second (Derek Lowe - 2.58) and third (Wakefield - 2.70) in the AL in ERA. They also would have still missed the playoffs, finishing 10.5 game behind the Yankees for the AL East title and 6 games behind the eventual World Series Champion Angels for the Wild Card...