Attached is a paper by George White which analyses the attendance at recent AMA Nationals and the results of the 2014 survey. A very simple précis is that:
a) the survey response was very poor
b) there is a clear preference for the 4-day event
c) there is no clear preference on Easter vs non-Easter.
George concludes that it should be up to the LOC to decide on the timing within a window set by AMA