I've been involved in various kinds of festivals over the years and have some experience "booking" name acts and "scheduling" local "play-for-fun" groups. These days, the "name acts" (not necessarily 'pro' in the sense of not doing anything else) tend to be groups with a CD that somebody on the committee happens to like. Sometimes, those groups do draw a crowd, but far more often, it is the "local" groups who have the more faithful fans who come pouring through the gates. The pro/am distinction is more about the business side of things than about music. "Celtic Rock" is the hot new thing at the moment, but that audience is small when compared to the folks who turn out to see their favorite "local" group.