I'd put something like the 3ds remakes of the Zelda games in that grey area. At first glance it looks like everything was just made to look a bit nicer (It's a remaster!) but if you dig a little farther you realize that parts of it have been either heavily tweaked or potentially re-implemented entirely (Maybe a remake...?). Same with the Diddy Kong Racing remake. It's 80% the same, but a bunch of new things were added, some mechanics altered, etc.. There are lots of things in between "some visuals were updated" and "we started from scratch".