When you loses wallet, it has the effect of removing money out of circulation. Lost bitcoins still remain in the block chain just like any other bitcoins. However, lost bitcoins remain dormant forever because there is no way for anybody to find the private key(s) that would allow them to be spent again. Because of the law of supply and demand, when fewer bitcoins are available, the ones that are left will be in higher demand and increase in value to compensate.
I don't think there are a lot of people losing wallet access though. It's real money we're talking about here and probably the only.time this can happen is when someone dies and didn't have the foresight to provide walet information to family or friends. Everyone's being careful now about their btcs since its becoming more and more expensive nowadays