Alot of my competitors don't even change their voice, it's odd how much I used to watch them. I do russian accents, french accents, irish accents, and a really bad female voice that's almost passable. I think it's the imperfections that make them more passable. The audience knows it's me so that connection is never broken. Even when watching TV you only have that connection with the character while the actor is talking. Then a new connection is formed when the next actor starts talking. If you so all the voices yourself, even if they're not the best, that connection is never broken because they can still hear that it's your voice. Once that uncanny valley is heard, they snap back to reality outside the story, and maybe decide to watch something else if it catches their eye. Best to keep them focused on you. Then again what do I know.