Personally, I think the focus on hymns and little instrumentation in Sacrament Meeting is a position taken in opposition to what is perceived as over-emotionalization in worship - a substitution of emotionalism for what we perceive as spirituality - a perception of emotional manipulation compared to encouraging the still, small voice.
I wish we were more open to expanding our musical experiences in church, but I also believe there is deep truth in the concern. That belief is reinforced every time I see the commercials here in my area for a "church that rocks"
I believe if the CHI was understood better (especially the difference between "should", "may", "some", etc. and "shall", "must", "never", etc.) and followed more closely (especially the constant call to follow the Spirit in making real-life decisions), it actually would loosen up the Church not just musically, but in many, significant ways. That's a different post, however.