Jackie Speel has sent me a note, regarding her suggestion that the VM might be a puzzle book, in the vein of Kit Williams’ Masquerade or Mike Wilks’ The Ultimate Alphabet.
I’m moderately unconvinced that this is the answer, but Jackie has also pointed me to two wikis she maintains, namely the Voynich manuscript Wiki and Voynich Wiki. I have not yet had time to look deeper into those two wikis, but at a first glance, they seem to contain quite an amount of compiled information. Check it out!
Thoughts about the Voynich Manuscript 
I would be interested in reading Jackie’s theory. Is it modern as the examples you link? Will you be posting a summary of it? Or does she have a site about this theory? I have not thought of the Voynich this way, but on a (possibly?) related note, I would love to hear her feedback on the “puzzle root”:
Hi Rich, the jigsaw puzzle root is one of my favorite finds of yours. So to maintain my ‘true faith’ I am looking for alternatives :) The best I came up so far is rope-maker.
http://ellievelinska.blogspot.com/2013/05/the-voynich-manuscript-clematis-vitalba.html
I am not sure if the VMs is a game, but it is one heck of a puzzle :)
All the best! Ellie
I don’t know about your rope-maker root… maybe, if it was sliced so it is a “slab” like the VMs root. But not in its natural form. I like most of your comparisons, as you know, but this root is not close enough for me.
Someone else had suggested a type of African plant, with “wood” in its name… but I can’t remember it offhand. Was that you? I think that was closer. Not as close as the puzzle piece, of course!