"The value lies inherent in the song, not in the regional mannerisms or colloquialisms. No song is ever harmed by being articulated clearly, on pitch, with sufficient control of phrase and dynamics to make the most of the poetry and melody, and with an instrumental accompaniment designed to enrich the whole effect."
                                                                                     —Richard Dyer-Bennet

If a singer's diction is so clipped and precise that you notice it, that's too much.

If you can't understand the words of the song, that's not enough.

Don Firth