Imagine waking up tomorrow with the solution to the Voynich Manuscript.

[eggyk]

How do you distinguish a genuine discovery from the endless stream of speculation, projection, fraud, and self-proclaimed breakthroughs?

Honestly, I don't believe it's necessary to convince everyone, or even a majority of people to have your solution seriously considered. 

History is full of examples where practically all the experts in a field rejected what was in fact a correct and ground-breaking discovery/solution/invention.

Not enough is known for certain about the VMS for there to be a general consensus on its contents. Sure, certain individuals are and have been convinced of their own solutions, but I would say the consensus view right now is pretty much "I don't know" or "my mind is open to anything at this point".

With this in mind, I would say that convincing even 10-20% of all people that a theory is seriously plausible (not even convincing them it's true) would alone be a large shockwave through the community that would generate huge interest and conversation. The voynich community doesn't really have a 90% consensus on anything in particular, so if everyone disagrees, including those open to hearing the theory, it likely is either wrong, partially wrong, or does not yet have enough tangible evidence to be considered seriously. 

To get a theory from "seriously plausible" to "correct beyond any reasonable doubt" is probably a unnattainable goal. 

Frankly, anyone who believes their theory is correct beyond a reasonable doubt has likely not considered all of the ways they may be wrong. Just speaking statistically, out of all of the people who think have thought that way, what are the chances that I am the odd one out? Only the most undeniable, slam dunk discovery like "I found a hidden signature that reads 'Written by W.Voynich - 1905'" would make me think that way at this point. But even then, I would expect due process and critisicm on even that discovery.