I believe voice quality of actors is too frequently overlooked. It's the primary means of conveying their characters.
As for TPM, it never bothered me. The voice added an unusual quality and point of interest.
NP stands out as having a particulary fine voice (since maturity-post TPM) IMO. I've heard her speak on the bonus discs and a few other occasions and her casual speaking voice is even better than her movie voice- so it's not the work of clever sound editors.