Peter, you are right about what I want to be able to do with these pictures.
I've tried scanners. Problem is they introduce a lot of glare because the light does not come in at an angle - the very thing you suggested with a photographic stand. Most scanner won't be able to deal with an A2 or A1 size piece. For that matter, most scanners won't be able to deal with A3. Also, scanners also struggle with the nature of my work - subtle white details on black paper. They are not able to pick up the subtle nebulosity details - low contrast on a very dark background. This is why I've gone down the photographic route.
I have the lighting set up exactly as you suggested. I even do this with my sketching at the eyepiece for the very same reason - to reduce the amount of glare coming off the page. Funny enough when people come up to me while I'm sketching, they first stand directly opposite from where the light source is pointing, so they don't actually see anything and wonder how I'm actually doing this. That's until I make them stand where I do while I'm sketching - then everything makes sense...
Anyways, when so many of the sketches involve gossamer-like soft nebulosity, like my recent piece of the Flame and Horse Head, a scanner just wouldn't be able to pull the nebulous detail:
I wonder if it's not just a matter of looking to try a larger format chip in order to suss out their capability compared to my own SX60. As you mentioned, from up close my camera does very well. The problem comes when the camera is set further away. Reason why I'm asking about larger format cameras is because of their ability to pick up wee details, such as pinpoint faint stars while photographing the Milky Way.
Anyone have a camera I could try? I'd be happy to bring the piece to your place for this as you would be familiar with its settings, and is a precious bit of kit. I could bring two or three different sketches to try out different scenarios.
Alex.