Your sewing room sounds like mine!!! Can't count how many times I needed the fabric near the bottom and had to unstack everything on the top to get to it, then re-stack it.
Anyway ...
As for saving space, it will highly depend on how well the space is utilized. If for example your shelves are 12" high and the comic boards are only 10" high ... you are wasting 2" on every single shelf. But then if you know your shelves are 12" high you can get *something* (corrugated plastic for example) cut to within a 1/4" of the shelf height to better utilize space.
My plan is exactly as yours ... I want shelves built to store my fabric on boards in an upright position so I can easily see what I have and grab what I want. I'm disciplined enough that once I am done with the fabric it will go back where it belongs.