Can Shielding Wards work with Clean Slate scrolls?

To gain slots they previously lost on their very well-scrolled items? With 20%s of course. edit: but I see your point in that it's not really worth 11k~ NX just to get a slot back.

Pretty much.

I mean, I can imagine there are situations in which someone -might- have great Potential on an imperfect weapon, but, especially with all the GM Scrolls flying around, it probably would otherwise be cheaper just to make a new one.

Of course, your mileage may vary.