yes, you should do some minimal, just barely visible sharpening upon capture. You should scan at full size, do a tiny bit of capture sharpening, do all your editing at full size, then, when you know what size you want to output, make a copy at that resolution and size with additional, appropriate sharpening. Only use that file for that size and that resolution. Period. If you decide to print bigger, then do it again.
And, to be blunt, if people are scanning with any scanner, with any scanner software, with the intent/hope that the output scan will be the final result, then they aren't taking their scanning seriously. Do you just do contact prints for everything, all the time? And if you do, is that because you chose to do a contact print and expected that print to be the final version, or did you perhaps have to make a lot of adjustments prior to that to get it the way you wanted?