Great sound possible using a Subwoofer?

My speakers are flat to 38 hz but I feel I'm still missing impact, power and weight on most of the pop/rock CDs I listen to. I don't know if a high quality subwoofer would be a positive addition to my system or just add unrealistic bass and muddy up my midbass and midrange. If anyone has extensive experience with this dilemma please tell me what you think. (would better isolation of components, cables or power conditioner help the low end?)