Getting together with other people and making music is one of life's great joys. Listening to others do it just doesn't compare. So it's definitely worth it to address the problem of overly-loud festivals.

Can you take some other approach to finding a quiet place for acoustic music? How about early in the day (but not too early) before the acts get started? Or how about a hike to a friendly location such as a church hall or a school?

Even renting a bus and spiriting the acousticians away would be cheaper and simpler than building and hauling a shelter.