I can definitely relate with you. When I see a band live, one of the things I love most about it is seeing them enjoy performing. Especially if we're talking about a loud rock band as opposed to an acoustic guitarist or a smal jazz group (although Thelonious Monk was a notoriously good dancer...)
As far as the difference between the band members, it can be tough to seem involved when we're confined to our drum throne. But I definitely hate to see drummers hiding behind their kit, totally indifferent to the music or the audience. Like pollyanna said, at least the frontman/woman should feel the need to engage the audience more. I think it naturally adds so much energy and feeling to the music. I've played a gig as a guitarist/singer before, and I felt that moving my body with the music and making eye contact with the audience helped me get into the music more easily.
This thread reminds me of a video...