The fact is we need the speculators. The speculators keep the trade volumes high enough to ensure liquidity of your BTC. Without this there would be much trepidation from casual users - if they know it is very hard to exchange their BTC why would they want to accept them as payment? The speculators will move in early, just because they know other speculators will follow! So it is really the speculators that bootstrap the currency valuation as I see it.

Could you explain this a little better. What would prevent someone from doing some large transactions with themselves in order to manipulate the price?

A great deal of the attraction to BTC in the first place is that you do not *have* to trust any central authority or server. So, just use their wallet for money you are actively exchanging through them. Use your own encrypted and backed up wallet for your "savings" account.