In Vuescan, I always have a bit of room to either side of the histogram, meaning that I've captured everything I can out of that negative. Also, since I can apply different, pre-deteremined film/dev contrast curves, I can produce slightly different tonal scales _and_ combat thin or thick negatives on a per-frame basis.
Finally, it is wise to avoid using any sharpening, in my opinion, at the scan stage. I use sharpening in photoshop initially just to bring it up to a basic level, then smart sharpening based on output size when printing.
allan