Could there be more documents written in voynichese ?

[Koen G]

Even if there were other documents written in Voynichese, and if any survived, and if they were discovered, and if the discoverer were sufficiently familiar with the VMS or sufficiently curious to bring them to wider attention, and if they were then digitised and made available to Voynich scholars (a lot of ifs) the likelihood is they wouldn't bring us any closer to solving the VMS. We already have a huge corpus - much larger than most ciphers or untranslated writing systems - along with labels and pictures. More of the same is unlikely to help.

I both agree and disagree with this. Even if we were to double or triple our corpus of Voynichese text, it wouldn't bring us closer to a solution and we would still be left with the same questions we have now. 

On the other hand though, any new Voynichese document we'd find has a high likelihood of being special.

Either it's a different document written in Voynichese. In that case it could be accompanied by drafts or notes giving us insights in the process, as Rene says.
OR, it could be pages that have once been removed from the MS itself. We know that there are many, from various sections. Maybe even entire sections we have nothing left of. The thing with these removed pages is that they did not fall out randomly. They were removed for a reason. If you're desperate to have Kircher solve your unreadable book, do you send him some generic pages or the pages you think that, for whatever reason, are most likely to lead to a solution?