So I suppose the difference here is that currently both boards are open, whereas you are potentially looking at shutting this one down (let's be honest, if the new one takes off, there will be no going back). So I would say that the posters on the other board actually *aren't* entitled to a say, as their board isn't at risk of being shut down. I would say that the only vote should be on this forum.
As things stand, I'm minded to give the new one a go and, if I like it, I'll vote to go over there permanently, but fairness is important here.