People kept spending because there were investments available (housing) which outperformed bank interest rates, 401k's, and pretty much everything else. There was no incentive to save because they were saving merely by owning their homes. This happens when there are bubbles. I don't see how the Bitcoin economy is immune to them, so you wouldn't have actually avoided what happened merely by using a different currency.
Nope, it was overborrowing. One of the reasons that the economy is sluggish is that consumers are underspending.
>> it has reached its maximum of 21 million bitcoins, the deflation should be a lot smaller
That's when deflation in bitcoins will get worse, because while wealth will increase, the amount of currency in circulation will not.