I'm very excited to hear that our own Dr. Stuckwisch is set to discuss this issue among others at the ACELC free conference in Austin. He asked us fellow Gottesdienst editors to chime in as he prepares his paper. Here's my stab at it.
Indeed - it's a bit like the judge's famous quip about pornography: hard to define, but I know it when I see it.
Anyone who uses the hymnal for the service, the lectionary for the readings, and vests in alb and stole is traditional. A chasuble can also be traditional. A little bit of chanting - like DS Setting I's Kyrie, can still be traditional. Bowing at the consecration can still be traditional. But if you have the chasuble, a little bit of chanting, and the bowing...that's starting to add up to High Church.
Anyone who uses the hymnal for the service, the lectionary for the readings, and vests in alb, stole, and chasuble, and chants all the parts where the says it "may" be chanted or spoken is High Church. Genuflecting during the Creed and/or the Consecration is High Church. Incense is High Church. Having an assisting pastor vested in dalmatic is High Church.
Traditionalists are conservatives and can thus suffer from the conservative's bane: what am I conserving? Like the GOP who is always trying to conserve the status quo of 20 years ago, which was the progressive vision of 40 years ago, it can be hard to know what they stand for. 50 years ago the alb was High Church in the Midwest. Today it is traditional. Thirty years ago a chasuble was unheard of. Today the utterly traditional, "low church," say-sing parish where I vicared has chasubles.
Folks who are High Church can suffer from the repristinator's bane: setting a given point in history as the high water mark for good practice and seeking to regain all those ceremonies.
Intelligent and well meaning folks in each camp focus on an honest to goodness agenda: I want my practice to reflect my doctrine and to teach the people all while honoring the heritage of my church's history and making realistic accommodations to the sensibilities of my flock and my neighbors. A good many men in Missouri have exactly this praiseworthy agenda and thus we see the creep of ceremonies that were once the exclusive property of the "High Church" (chanting, albs, chasubles, Tenebrae Vespers) into the realm of the "traditional." All this really means is that Missouri has slowly reclaiming portions of historical Lutheran ceremony in a responsible way that teaches the people and confesses our faith clearly. I view Gottesdienst as a resource for anybody with this agenda, whether they are "traditional" or "high church."
Reading the Braunsweig-Wolfenbuettel Church Order was the real eye opener for me. It turns out this High Church/traditional, or more ceremonious/less ceremonious distinction has always been with Lutheranism. In that Church Order the divide is spelled out with amazing clarity: the rich city churches had Latin and high ceremony, the poor country parishes had low ceremony and Luther's (in my humble opinion: grossly truncated) German Mass.
We are a society of the middle class. It is only natural that our church's have therefore mixed up the city mouse/country mouse divide.