From your post it sounds like you are scanning photos, and not negatives. If that's the case, there is no need to scan at much higher than 300-400dpi. A photo has very limited detail, while a negative can contain very high resolution details that would warrant a 3200 dpi scan.
The human eye can't perceive more detail than ~300dpi in a print, even up close, so if you are not intending to enlarge and reprint the photos this would be sufficient to archive the image. I also doubt that there is much more useable resolution in the photo than 300-400dpi, the paper just won't hold that much detail.
Try a 300 dpi scan, a 500 dpi scan, and a 1000 dpi scan of the same small section of print. Compare them side by side on screen and see if there is really any useable resolution gained by going to higher dpi's. I would guess that there is not.
Hope this helps!