That fact that most have already been computed has little bearing on the future price of BTC. What matters in the future is whether or not people will actually use Bitcoin as a currency (it has no other use); I am still not convinced that it will ever become mainstream. I hear about all sorts of places that accept Bitcoin payments, but I have yet to see anything that matters -- I cannot buy diesel with it, I cannot pay rent with it, I cannot pay utility bills with it, my local supermarket does not take it, and I cannot pay taxes with it. Even for black market transactions (drugs, guns, etc.) Bitcoin is obscure; even with all the sales that happen on Silk Road, you are looking at a tiny fraction of the market for illegal drugs.
Bitcoin is in a very precarious position. Most of the cost of buying in is the result of speculation about its future use, which is fueled by the media coverage it receives on tech news sites. A lot of the hype is based on questionable assumptions about Bitcoin's security and about the lack of authorities in the system. Bitcoin's ability to survive when the hype dies down and the assumptions are challenged is doubtful, at least from where I sit.