Do you have a record of when you unbanned and rebanned these sites? (I keep a website log of changes, so I can look back, sometimes months later, to find the origin of any changes in long term trends).
If you have that record, I think it would be great to write up what happened and send your data to Google. I suspect it is difficult for them to do anything about unspecified or general observations/complaints. However, I've found them to be appreciative of well-presented, hard data, probably because that's something they can investigate.