A good friend in Atlanta is many times more tech savvy than I am, he has had some very underexposed Kodachrome slides -- which he scanned several passes and was quite surprised at the detail and quality that resulted. I believe he was using a Coolscan. Check to see how to do multiple scans on those dark slides.
Many of my slides faded, the ROC function did an excellent job of "restoration of color", and the Digital ICE worked well-- even on Kodachrome. There is a setting for Kodachrome with the Nikon software, though sometimes it toggled itself off, yet the results were good.
Agfachrome used to have a good reputation for reds, plus I got a good deal, so I bought 30 rolls for my first western trip. They were processed by Agfa, yet they faded very badly, and the Coolscan saved the images with excellent correction. They can be further adjusted with Photoshop.
I believe I received a Signet 50 Kodak when I was quite young, yet well after these were shot, and I recall the ASA was 10? My first roll was not so good.
Also, some of the non Kodak processing labs were not so careful, and the drug store processing did not help.
After scanning perhaps a thousand of my slides, I began to "save" the rest for another day.
Hope the free advice is worth the price.
Regards, John