As a savings vehicle, depreciating currency (i.e. bitcoin) is an ideal place to park assets. Why in the world would I, or any other sane person spend the coins, knowing that tomorrow, they will have greater value.
There are 2 factors going on here.
One would be Gresham's Law where "Bad money drives out good", in that all the world's fiat (the bad money) drives the good money into hiding.
The second factor is that bitcoin appears to be a giffen good. As its price continues to escalate, more people will want to own it.
As a business owner, I'm thrilled to be paid in bitcoin. As a saver, I'm loathe to part with these precious gems.
I don't think bitcoin is a depreciating currency. Greshams law basically says: if people have something they don't want, and they can give it to other people to get something they do want, then they will do do that before they give up something they want more. It's quite good for Bitcoin's future in my opinion.
Once again, this is NOT what Gresham's Law says.
Gresham's Law is only considered in cases where two currencies are fixed in price to each other, not by economic means (free market), but by political means.
The undervalued currency will be hoarded, and the overvalued currency will be favored for transaction.
