Looking on the archive section of the club website, I see average home attendances from 1979.
I wonder if failing to get in the league in the 2 years as APL champions put a lot of fans off, as attendances dropped from 1900+ and 1700+ in those two years, to just over 1000 for the next 5 years. Bear in mind some of these low-attendance years saw some big FA cup and Trophy runs.
Interestingly, the year following John King's (first) departure saw an average home attendance of 1466, which dropped just a little to 1349 the following year (Tommy Doc!) I seem to remember, certainly in 86-87, that there was some deal where children got in free. Anyone confirm this? Apart from the "nearly" season of 90-91, attendances have hovered around 1000 for conference, less for the tier below.