In the sentence you've given they mean exactly the same thing. They aren't always the same, though. If something is precious to you it means that it is of great importance to you. If your childhood sweetheart spends a few cents of his pocket money on a ring for you, then that ring is precious. It's not valuable, but it's precious.

There is not much difference. They are synonyms. Valuable may suggest monetary value more that precious, but people do refer to precious gems (diamonds). Precious may suggest sentimental or emotional attachment more than the other, though I might also say: You are my most valuable advisor.