The issue confronts every parish. Should parishioners experience different music at different Masses or the same at every Mass? I will tell you my view upfront: the attempt to create uniformity sounds good in theory but it nearly always leads to disaster in the present context. To see why, we need to understand the background.
This background concerns an issue that has emerged in the last thirty or so years. Sometime in the 1970s or 1980s a pastor set aside one Mass that was called the folk Mass or the youth Mass to experiment with all the new material being sold by the big publishing companies. Usually, this was prompted by a pilgrimage that some song leader took to a conventional or workshop somewhere and came away impressed by how the jazzy stuff seemed to energize people in some way.
Meanwhile, not everyone in the parish agreed. They held on to their traditional hymns. In many parishes, two hymnals eventually populated the pew racks. Their different colors and styles symbolized everything. It seemed like two churches in one parish, but everyone more-or-less lived in peace. The "divisions" in the parish make people feel uncomfortable but no one had the strong desire to do anything about it since, after all, most people were rather happy with the "divided parish" model.
At some point, disaster strikes. A new pastor arrives with a new musician or liturgy director in tow. They look at these hymnals and see how the parish is split and think: this has to go! How can we lead a parish without unity among the people of God? So they call all the musicians together and announce a new plan. There will be a single Mass setting in all Masses. We will all sing the same hymns each week. We will gather in committee to make decisions. The various choirs can do different music for offertory but otherwise, the central plan must prevail!
And what is this plan? It is to have some traditional hymns, some contemporary hymns, a standard Mass setting that splits the difference between styles, and each Mass will have a bit of piano, a bit of organ, a bit of guitar, and so on. This is what is called an eclectic approach. The musical results are not impressive of course: it produces a mish-mash of styles that might be uniform across the parish but is un-united within each Mass. All channels for experimentation and progress are now closed. That's the musical and liturgical cost.
The human cost is far greater. No one will be happy: not the traditionalists, not the contemporary-music people, and, in fact, none of the musicians. In fact, it will break their hearts, and that goes for both the people who love chant and the people who love to strum to the latest offerings from the commercial publishers. In the committee meetings, they might arrive at consensus but no one tells the truth in a committee meeting. The appearance of consensus is an illusion that evaporates minutes after it is over.
It might seem viable for a few weeks or months, and then the dam breaks. Musicians leave the parish. Choir members stop attending because no one wants to sing music he or she hates. The talented organist quits. The guitar players take off too. All that remain in the end are the unprincipled people with moderate talents who will do anything for a small paycheck. They lead a handful of undiscriminating singers. If this situation persists, the meltdown can become total and spread through the entire parish, so that people no longer know which Mass to attend to escape the music they hate. The parish is united only in its seething anger at the interlopers who upset their ways.
People can theorize all they want about united parishes and bringing everyone together, but this is an apodictic truth that no one can change: Catholics are attached to particular Mass times and have absolutely zero interest in what happens at the Mass before or after. Each Mass time is associated with a specific demographic and culture. It was always true before the council (Low Mass, High Mass) and it remains true now. These modern-day Robespierres who attempt to change this might as well try to reverse the flow of the Mississippi.
What is the right approach? Diversity. This permits progress to occur in increments, peacefully. Each Mass time learns from the other. This allows for experimentation and when something doesn't work, it affects only one Mass so the damage is limited. Also, inevitably, competition develops between the crews of people working in specific times. This is a good thing actually, not a bad thing. Pastors who permit this to develop normally and naturally are wise indeed.
This is particularly important for young pastors who desire a change toward sacred music. Such a transition absolutely requires at least one safety-valve Mass that permits people who hate chant and plainsong, not to mention traditional hymnody, a chance to do their thing. People vote with their feet and their dollars, and the patterns of Mass attendance do not go unnoticed. Not to worry: change will come in time.
Another major benefit of letting different Masses do different things is that this approach takes power away from committees. Actually, the goal should be to never permit another committee meeting to take place. Such committees accomplish nothing. They should all be abolished and immediately. This saves time too. Everyone will be relieved.
Remember that it does no good at all to drive the strummers out of the parish. It is their parish too. They have made a contribution over the years and don't believe they have any less right to be there than anyone else. They need to be brought slowly and surely into the current environment in which sacred music is making great advances. Moving too fast and too comprehensively risks losing a chance to do wonderful things over the long term.
That still leaves the problem of Holy Week liturgy of course. What do you do about that? There is no final answer, but many parishes have found peace in specialization here too. Let the contemporary group do Holy Thursday and the chant group do Good Friday. That leaves only the Vigil but surely something can be worked out here year to year with gradual change toward the good.
Parishes are a bit like families in which change occurs steadily and even unnoticeably as people grow up and become older and wiser, and new young lives emerge to remind us that time moves forward and that we will must all eventually leave the faith in the hands of the next generation.