I have got into a fairly routine habit with my scans. I can’t afford Photoshop so use Paint.NET for adjustments.
I scan at 600dpi and save as 80% JPGs. This gives very high quality but without the huge file size of the PNG. I play my music on a 50" TV screen so the artwork details are important to me.
The matrix may get a 1200dpi scan to get the mould details.
I tend to avoid much post-processing. A bit of a tweak of the brightness. A slight twist to make sure everything is straight. I leave damaged covers visible as these are more real.
There are a number of threads like @psychoadept has picked out. Also a few articles at Discogs if you want to go into overkill of perfection. Though don’t be put off by the way some people will spend hours on each image. The important thing is to get an image that someone else can use to confirm they have the same copy. Remember - MB is about identification first, not about tagging.
With me it is a time issue. If I have a whole release to scan including booklet that can be quite time consuming. That is at least a dozen images - often more if it is a big booklet.
Usually I’ll keep pages as a pair, other times I’ll split to separate pages. When uploading pages I’ll always add a note as to page numbers.
If I don’t have time to do the whole booklet, the most important pages to scan are those with the credits on. But it will still take me an hour or so to get through the scan, save, edit, tweak, crop, uploads.
I do fine it a little funny uploading a cover and knowing other people planet wide now have my cover with their music.
With KODI and displaying the images - my theory is “be prepared”. KODI’s artwork handling is getting more advanced on the art side. Dave has added in a lot more links for the skinners to get at this art, but the still seem to be settling on the hows. So I keep scanning and expect more use of this by KODI at a later time.
Boxset handling is an example of this. I have all kinds of box sets with different art for the different discs. Black_eagle is now working on making use of that artwork. When his code becomes available, then I already have lots of albums ready to make use of it.