You've raised some interesting questions and I'm not sure of the answers, but here are my observations for what they're worth.
I've seen before and after shots on the net, calibrating one's scanner with an IT8 target, and the differences seemed to me to be rather subtle. I am guessing that such differences are similar to the differences one might expect between a generic printer/paper profile for a particular model of printer and paper type and one that's custom made using the actual printer. Futhermore, if one is advertising such differences, either to make a point for a tutorial or to sell a product, then one would choose the more dramatic difference as an illustration.
If I was scanning recently exposed film I'd probably take the trouble to calibrate my Elite 5400ll and create individual film profiles using, perhaps, Wolf Faust targets.
As it is, the results I get are so variable with the same type of film, because of fading, I can see no point in any calibration attempt that results in a subtle difference at best, with recently shot film. For example, it's sometimes not clear to me whether a particular slide I'm scanning is a Kodachrome or an Ektachrome. Vuescan offers 3 film profile options for color positives; generic, Kodachrome and Ektachrome. Switching between Generic and Kodak always produces a noticeable difference (for better or worse), but switching between Kodachrome and Ektachrome can result in no discernible difference at all. I assume because fading has made such differences between these two film types irrelevant.
Nevertheless, it is useful if the scanning software includes a number of film profiles. However, the situation seems to be that the incorrect profile can sometimes produce the better result.