This may be a crazy request, but in my days as a graphic designer, in Illustrator you could hold down the TAB key and it would remove the guides and frames and such. I got very used to this and found it helpful to find errors and left over stuff.
I think it might be helpful in Dorico too. If, when in Engrave mode, you could press TAB and have all the grids, signposts, highlights and all go away so you can see what it will look like when printing. Just a thought.