Russo,
I've always viewed scanning as an archival process. You are migrating an analog image to the digital world. Archiving it if you will. You already know the scanning process is very time consuming, so if possible, I try not to do it more than once. I always scan at the highest resolution and best possible quality. I usually even keep the original scans without color corrections, density, curves, or other enhancements because advances in software (and my editing skills) may allow a better image to be made from that original scan in the future. I do "spot" the original scanned image. (remove the dust spots, hairs, and other junk that wasn't actually part of the image-Again, so I don't have to do it more than once)
Of course, if you get better equipment or your scanning skills improve markedly, that would be an excellent reason to rescan some of the images you did in the past that might not be at their best.
I take that highest quality image and make all the digital copies I need for any purpose. You can easily make downressed (downward resolution-larger to smaller number of pixels) copies of a digital image with no loss of quality. In some cases things like grain are minimized in the downressing. You can get a 360 DPI image to send to a printer or a 1024 pixel wide jpeg for this forum by doing the resizing in Photoshop or any other image editing program that will work. I normally wouldn't do it in the scanning software.
You seem in the market for a scanner. You mentioned you have an Epson V600 earlier in the thread. A good scanner, with one limitation. Epson is living in a fantasy world regarding the resolution their flatbed scanners can actually reach. If you check the filmscanner.info site, you will see how their test turned out. My V750 suffers from the same problem. Since I use it to scan large format film, I do okay even with the resolution issue.