It's an interesting one this. As I've posted about elsewhere I've been having real problems with the SI recently, out of 1,300 indexed pages only 100 or so are currently in the main index. However: -
My traffic is actually up from what it was when I had 500 pages in the main index. I'm getting about 1,000 unique visitors a day now, and earlier in the year before the problems started I was getting around 700.
Part of this could be the Christmas factor, and the fact that there are just a greater number of people searching for my products. I gues I will have a clearer indication of this in January, when it may well be tumble weed central
The thing is though, it seems logical that if the pages were not supplimental then I would be getting more traffic as they would rank higher??? With this in mind I will continue in my efforts to get the pages back into the main index.