I'm afraid clashing is the bane of an organisers life. A major factor for the smaller festivals is catering for the hard core followers. WHFF and Moira are a classic case, many who go to either really want to go to both. Dave E's answer of alternating is one solution. But this means that the fun chat about what happened last year, is meaningless; who talks about the year before last?

Early planning and chat between organisers, including the big boys, is surely the only way this can be sorted. The idea of hanging on to a specific weekend might have to be relaxed, you just tell us when it's on, we'll be there.
Is this not part of the idea behind AFO (the Association of Festival Organisers for those across the pond)?

P.S. We will be at Moira, sorry again Dave.