In 2004 and 2005 North played Eagles at Prospect late in the year. Both years it was the ABC match of the day and the weather was inclement both times. The crowds were 3044 and 2879.
Thus if the Crows hadn't played it is fair to assume that the crowd would have been in the vicinity of 3000 at least. I knew of a few North fans and at least one Eagle fans who went to the Crows.
The problem really is the AFL, Adelaide AFL games always have smaller crowds than at other times over the weekend, but I think that if the AFL does schedule a Crows game on Saturday afternoon in Adelaide, then the SANFL should schedule a Port game at Alberton to have the least impact on SANFL crowds. It ain't rocket science.