When I scanned B&W film, I had the same problem. I treated to difficult spots with Photoshop's healing brush and had good success using Photoshop's Dust & Scratches filter for dust in zones without details. The trick was to first select the zone to treat with the lasso, so that it would not destroy detail elsewhere. You need to use the Radius and Threshold cursors to get the desired result. It can still be tedious because you'll end up selecting small zones, treat them and repeat, but the result can be very good.