The original Frederic Goudy quote that I'm riffing on:

"A man who would letterspace the lowercase would fuck sheep."

This is usually rendered as "steal sheep" to... er... protect the delicate sensibilities of young typographers? Anyhow, he was talking about adding extra space to the lowercase letters of serif type in particular, so go wild with your sans-serifs.

But seriously, if a passage must be centered like on an award certificate or diploma or whatever, I say one should use the "balance lines in paragraph" option, or lacking that, soft line breaks to keep the lines approximately the same length. (I like to fudge things a little to make sure phrases aren't interrupted, but that's a personal quirk.) I just loathe it when I see one or two long centered lines followed by two or three words dangling in the middle like untrimmed nose hair.