Lost Bitcoins is a good thing actually. They make your unlost bitcoins more valuable. (As long as the lost ones aren't yours of course)
I don't think so: nobody knows anybody has lost his coins, there's no way to know it, apart the case I exposed in the previous post, or by admission of the user himself, which can be fraudulent.
AT THE MOMENT the value of your coins is UNAFFECTED by lost coins.
In the future, when we'll hit the wall, THEN this may affect it, as less and less coins will be in circulation.
i presume that the impact would be very low on the market, do not expect an huge rise in demand only because 30% of coins are lost, people simply will buy less one whole btc and more satoshi or bits