SuperSystem was written from experience at very high stakes game where Doyle could run over scared money by playing loose aggressive. Low stakes NL hold'em is a different game where people call all the time and don't care about losing their 25 bucks

You also may have a hard time moving up if you're leaking preflop by playing too loose when players at 50NL or something finally start making obvious folds postflop and cut your implied odds off.