A good reserve QB is important regardless of your league rules because the position is extremely vulnerable to injury. Collectively, starting quarterbacks missed a total of 78 games last year and parts of several others. The same generally holds for second year men as well. Rookies and players coming off career years are generally over-priced in an auction. More than any other position in fantasy football, the running back rankings are the most diverse according to the rules by which you play.
Sanders is worth more in yardage leagues while goal line guys are worth more in touchdown leagues.
Third down specialists like Amp Lee and Larry Centers are worth a couple of bucks at the end of the draft because they have value only in performance leagues. Bid on these players according to your scoring rules. Remember too that roles change and that, more than any other position, running backs get hurt the most often. These types seldom touch the ball often enough outside the red zone to accumulate significant yardage or score more than five or six touchdowns a year to be considered for more than a dollar or two. But don't go overboard.