I'm striving toward this same goal, but with a much lower experience level, both from a darkroom and a digital post processing perspective. Like Ray, I tend to go for what delivers the most pleasing results, but one thing I've noticed after several months now of scanning slides and negs -- both color and b&w -- is that as my skill level improves, I often have to go back and redo images. This is almost always because I've overdone something in the processing, rather than underdone it. I have concluded that it just takes a certain level of experience to get to the point where I can accurately render images in scans.
I've found negs to be more difficult, generally, to get good scans of, because if they're underexposed even slightly, the shadow detail blocks up and noise, i.e. grain, is usually much more predominant.
I've used the Epson scan software a lot, though, and I've gotten to where I mostly use the gray eyedropper tool in the histogram window to establish both the most optimal color and density/contrast in an image. I might tweak the edges of the histogram after that, if it looks like it needs additional contrast adjustment. I have also realized that the more image adjustment I can do prior to the scan, usually the better the result will be. This is similar to the results I've found when adjusting digital images. There seems to be greater adjustment latitude working with the raw digital images before they've been converted to .tif or whatever than afterward. As for the Epson software, I haven't seen much point in setting up custom configurations or templates or whatever because it seems like just about every image poses its own unique set of problems or challenges.
Best,
Michael