Alan,
You can take some small consolation in that Levels before a scan is different from using levels after. Digital PhotoLab (the software I use) has a Levels dialog they call Histogram, and I do use it. However, I use it for a very gross adjustment. I don't get anywhere near the edges. I certainly do not use the droppers, which I think are the dumbest invention ever. Brightness/Contrast is also terrible. I ignore these totally.
The reason that Curves work is that its a curve, after all. When you move something on a Curve, everything else stays in an appropriate relationship. This is not the case with Levels, where you can be sure its clipping as you go. A great scan is made when you maintain al the tonal relationships, and expand the midtones, to contradict the natural compression of the device.
I am sure you know that you can add contrast to anything but taking it away is another matter. If there are 5,000 distinctions (just to choose a number) between zone 5 and 6 and you make that area very contrasty, you can cut the number of tone distinctions by 50-75%. You can't get those back by lowering a curve, or removing the contrast with a slider. Once you toss those extra tone distinctions away, they are gone. All great scans are a little flat. That way, the person making the print can add just the amount they want and they have the style of print they want.
Using Levels after the scan, say in PhotoShop, is just silly. Curves are powerful, and will keep everything in place...
Hope this helps.