The biggest mistake in almost any parish
In my experiences, the only parish with a liturgy committee that I've worked with that didn't butt into musical affairs was Holy Name. There was one representative from each department - myself for traditional music, a rep for the Extraordinary Form Mass (outside of music), a rep for the gospel choir (we never clashed, by the way - the gospel choir had their one Mass and I basically let them do their thing and they left me alone), a rep for decor, one for servers, lectors, you get the picture, and of course, the pastor. We more or less "reported" what we did and/or what we're doing in each department every other month. I had absolutely no problem with getting Worship - Third Edition into the pews there in 2000 (and the Music Issue out of the pews). Those hymnals are still in the pews at Holy Name today.
Unfortunately, this kind of liturgy committee was the exception.
Jeffrey Tucker has a whole skinny on your typical liturgy committee, the kind of committee a true organist/music director would find as the biggest mistake in parish liturgical life. The biggest nightmare committees are the ones that want to pick your hymns (I use that term very loosely in many of the pieces they choose), beg you to try some Haugen d'Hass (and I don't mean ice cream), or even want to pick your hymnals (someone just happened to get their hands on a Gather book and wanted to show it off to the committee - "Oh, look, MaryJo, ain't this cute? All Are Welcome! Doesn't that sound just like our mission statement?").
One could easily flash a copy of the Gregorian Missal. Now, THERE's a book with much more permanance than any hardbound hymnal from Adoremus to Worship to Gather Apprehensive. Why's that? It's the official chants of the Church, the music that the Church WANTS us to sing. It's singing the Mass, as opposed to just singing at Mass.
Better still, the hell with the liturgy committee! Go right to the pastor (hopefully he's supportive of good liturgy and not just "well, let's go ask the liturgy committee" - they typically won't make the right decision, even if they did know rubrics). After all, a really good priest will be your liturgy committee.