I understand where you're coming from, but isn't the whole point of bitcoin that it ideally should be decentralized? Alas mtGox seems to be dictating the price at the moment as this is the largest exchange with the most trade volume.
The structure that you suggest, would it not cost a lot? And how would we pay for it? Fees? Banking fees is something bitcoin is trying to avoid.
I don't understand this sentiment - the allure of Bitcoin isn't that it
is always decentralized, it's that it can be if you want it to. You decide the level of trust you want to have. If you trust almost no one, you run a full Bitcoin client connected to a few trusted nodes. A step up from that, you're running a chain-less client that has to trust wherever it gets it's balances from. Continue up the ladder until you reach whatever Bitcoin will eventually call banks.
Same goes with mining - yes pooled mining is essentially doing away with the decentralized auditing and blah blah blah... who cares? The fact is that there are plenty of smaller pools to choose from, and the bar is still adequately low that almost anyone with an upper-middle-class disposable income could setup a pool if they so chose to.
Bitcoin isn't about "my way or the high way" in that respect. It's also worth noting that plenty of people are already using places like MtGox as a Bitcoin bank for the exact purposes put forth in the OP - the system just isn't very good yet.