IIRC it was down to about 20K by last day. Before that it was at various times 24K, 28K and over 30K. I'm sure Dave will confirm/rubbish what I remember.
When full, the old Holte End was the most awe inspiring sight in British football. The Kop at Anfield, The Stretford End at Man Utd or the North Bank at Arsenal were minnows in comparison. Bottom right for me, with the lads from the Yenton.
Remember jumping the turnstiles in 89 to get in game v man united , and 1994 being in there for last game , great days
It was certainly 28k in the 70's, remember the game v Sunderland in second division when 58k in the ground and several more thousand outside the ground from both teams