"Accommodation at Whitby this year was not full. Last minute vacancies for the first time I can remember."

Strange. I crossed and re-crossed Whitby several times a day, and I can honestly say that I didn't see a vacancy sign. And when I inquired about booking for next year, I found that my flat had already been booked.

Landlords and landladies are usually confident that they can fill any last-minute cancellations for Folk Week. Of course, the vacancies you found may not have any connection with Whitby Folk Week. And they are certainly not enough to establish that WFW is declining year by year.