I agree with several of the above comments, and most seem to agree that the lower the distortion, the more accurately the source material, including the soundstage, can be reproduced.
Along those lines, I would say that vibration control, and especially of speakers, can also contribute to a better soundstage. Speaker vibration tends to produce distortion that is referred to as a "smearing" of the sound, and controlling it can reduce or eliminate the issue. Among other positives, I noticed a better defined soundstage after having employed Isoacoustic Gaia under my speakers.