Voice acting is one of the super rare meritocracies left. You can't sleep your way to the top or bullshit your way to the objective. Networking really helps (especially at the upper echelon of agent representation) but on your way there, you can either do it or you can't.
Im not looking to get into voice acting at the moment, but I do love what some actors are capable of doing with their voice. For example James Gandolfini, his voice is completely different as Tony Soprano from his real life voice. Granted, he has voice and dialect coaches, but ANY book or video that can help me even begin to learn how to manipulate, open up, free my voice etc would be helpful, thanks! And, good luck with your new career.
It's really the acting part that matters in the end. :D