I wasn't aware of the issue in the UK with thin glass. (Of course, truth be told, there are a whole lot of things I'm not aware of.) Is it possible to get thinner glass through other avenues, as with some of the more dangerous chemicals? You're spot on about the problem with some of the smaller format plate holders -- especially when a nice, thick coat of emulsion goes on. It would be a shame to rule out small plates because of glass, of all things.
You shouldn't experience any problems reusing unexposed plates. I've read of problems when exposed and processed plates were reused. Apparently, you could sometimes make out a faint image of the first exposure under the current image. This phenomenon was used by spiritualists to prove there were ghosts that could be photographed by someone with the right 'connections' to the Afterworld. I take that with a grain of salt, mostly because it's just too great a story, and because I haven't found any collaborating info in scientific publications (which doesn't mean it's not there yet to be found.) I've reused plates with no problem, but I don't use plates that have been etched and subbed before coating. It seems to me that may make a difference.
If you and your wife could supply pre-cut plates with baby butt-smooth edges in a number of thicknesses and sizes appropriate for a number of formats, and they were a reasonable price, I can imagine diy plate makers would buy. Right now, I think the attraction of the process is coating the plates oneself, but if you made a killer emulsion, that might very well change. I think there's room for the cottage industry in this arena.
Do you remember the source of the info you read about retained images? I'm just sure at some point, I'll want to see if I can make ghosts walk the earth .