Context
Why it sounds like her
Mae West built a career on inversion: taking the prim moral of a proverb and turning it into an invitation. “Too much of a good thing can be wonderful” is that engine in one line — it answers the old caution that you can overdo pleasure with a flat, delighted “yes, and?”
That is exactly why it resists verification. The line is so perfectly in character that quote collectors reached for a source after the fact, attaching her memoir or a film without ever showing the words on a page. The honest position: the sentiment is unmistakably Westian, but the citation is missing.
She didn’t coin the proverb — she coined the comeback to it.
On the proverb she flipped
The phrase “too much of a good thing” was already proverbial by the late 15th century. Its most famous early appearance is in Shakespeare’s As You Like It (c. 1600), when Rosalind teases, “Why then, can one desire too much of a good thing?” For centuries it carried a note of warning. West’s contribution — whenever she first said it — was to strip the warning out entirely.