Howard, I suggested that EFDSS tried running one festival again, this would be the way[imo] to begin.
possibly a one day festival, possibly two, I disagree with you about a low key festival not appealing.
if it was marketed as a fundraiser for EFDSS, I guess 80 percent of members would attend, then try and appeal to dancers as well as singers, and then to those singers who like to participate in singarounds, with perhaps one major concert, plus all day workshops.
there are a number of towns that have good track records of hosting festivals and have suitable infrastructure,some of these were originally EFDSS festivals and might be worth considering at a different time of year.
Whitby,Norwich[UEA]? , Broadstairs, Lancaster[ Formerly Maritime festival] the former Four Fools Venue, all have suitable venues, and some of those have schools which might be available during holiday time[easter, half term or summer holidays.
but there are many other possible venues other than those I have mentioned , Which already have a festival and might be happy to accomodate a festival at Easter or some other quiet[festival wise] time , there only seems to be one[gosport] festival at easter at the present time .