How important is humidified guitar storage?

It’s the most vital part of consistent play. Wooden instruments are at their best when stored in a stable humidity environment between 40 and 60 RH (relative humidity). The stability and moisture standard where your instrument was made is the same standard recommended for storage. If the humidity in your instrument case fluctuates or falls lower than 40 or higher than 60, the geometry of the wood changes, which does all kinds of bad to your pride and joy. Check out this video from Bob Taylor on what the zero-maintenance, 2-way humidity control of Boveda (formerly Humidipak) means to him.