"Speech is silver, but silence is golden":
We have exactly the same proverb in French (la parole est d'argent, mais le silence est d'or).
Even if it came to Britain in William the Conqueror's suitcases, the fact that it is still used in English shows that silence, at least on some occasion, is more valuable than speech.
I found this very interesting article:
From the Egyptians to shakespeare, it seems a lot of different cultures valued silence.
So I'll speak no more...