First of all, lyrics are a part of the music. Secondly, as I've already said, it depends on one's own personal values. The image that a band portrays for themselves represents how they intend people to see and to judge them. If bands didn't think that image mattered, they wouldn't bother having an image, would they? I think that immediately says enough to support the argument that image can matter. Also, more generally, the more knowledge that you have of a band, the band members, the way that they think and act, etc., the more informed you are regarding their music, which may expose you to things in the music itself that you weren't aware of before, which may or may not be a good thing.