Would Sidmouth be worse off, without all the "Big names", whom you can see/hear ad nauseam, at dozens of other festivals every year?
This would leave the ceilidhs, and the fringe events, official and otherwise. I'm quite sure that Sidmouth wouldn't see much of a decrease in visitors.
It would cost a lot less to run, so possibly the nett result would be, Sidmouth is better off financially.