Obligatory Simpsons quote:

Royce McCutcheon: "That's the miracle of the franchise. You get all the equipment and know-how you need, plus a familiar brand-name people trust. You'll be on a rocket-ride to the moon! And while you're there, would you pick up some of that nice, green moon money for me Royce McCutcheon!"
Homer: "No deal, McCutcheon that moon money is mine!"

I think you have this backwards. If anything, Google's share price should be depressed relative to its less opaque peers because investors are unable to accurately gauge the risk of investing in Google, which constitutes an investment "cost." Although Google's share price may be inflated because of the hype surrounding the company I think this is relatively independent of its secrecy. Even if Google was more transparent it would still be hyped (and no company divulges everything it's doing or planning to do).