If "rhetoric" means "the body of rules to be observed by a speaker, writer, or composer in order that he may express himself with eloquence" we do not quite see how it can ever become "too highly refined." That would be a contradiction in terms would not it? - something rather like "a virtuous tyrant."
When rhetoric becomes too highly refined, one has reached a stage of musical decadence after which revolution is in order.
"rhetoric" to me means "the body of rules to be observed by a speaker, writer, or composer in order that he may more accurately comport himself to the current notion of eloquence" -- meaning that the adornment of the language with rhetorical 'flourishes' becomes so elaborate that the speaker, writer, or composer can make an eloquent statement without saying anything at all about the state of musical material.
Ugh, the Teutonic Modernist rears his sluglike head again.