I've never been in the position of hiring music acts, but I have been involved in the hiring of numbers of persons. In every hiring situation in which I was involved, every candidate received a letter telling them of the results of the hiring, whether they were successful or not.

Many of them contacted us later, telling us how much they appreciated being informed. And several even contacted me asking what they could do to improve their chances of being hired, whether it was job skills they needed to obtain or merely better interview skills. And some even interviewed successfully for subsequent jobs and became valued employees.

I guess all this is a long way of saying that, although it's more work, letting every candidate know your decision and being willing to discuss their shortcomings with them will gain your festival a lot more good will than no answers at all. And, as I think was stated above, you may even find that some of the acts rejected this year will exactly fit the bill a few years down the road.