The reason I don't lose much sleep over defense is because I believe the primary and most effective way of preventing runs is having pitchers (especially starting pitchers) who simply don't give up very many runs. I'm a big believer in having bigtime starting pitching because, although a great defensive team will help you build up a nice shinny regular season record, when it comes to the playoffs, IMO, it's all about the starting pitching, and the better starting pitcher will generally win most of the time. And when you have guys like 15 Alexander, 08 or 10 Walsh, Russ Ford, Jake Weimer, Johnson, Maddux, Joss, Pedro, Koufax, etc., you're team isn't going to give up many runs, no matter how poor the defense is.
I did an experiment once by drafting a team with superior defense and range in order to see for myself if superior defense made a significant difference. Sure, I was among the leaders in defense, double plays and plus plays, but the bottom line is that the team was only a mediocre wildcard team with little firepower and second tier pitching and got knocked out in the first round. Why? Because the so-called defensive guys were expensive.