If your starting premise is incorrect, the rest of your assumptions will be wrong too.

Yes, people use Bitcoins to transfer VALUE, that's what all money is for.

But the value doesn't have to be expressed in fiat currency.  The more bitcoin
is widely accepted, the less need there will be to convert back to fiat.

People also use it as a store of a value, a hedge against inflation, and as you point out,
it is superior for transfer.  This has uses for remittances and ecommerce, and the
superiority lies in its divisibility, speed, and low cost.  Many would
like to see it become the dominant form of money, or at least money that they would
personally use.  

Some people like it because it can't be confiscated, nor does it rely on third parties.
It can be easily hidden and moved across borders.  There's so many advantages
over fiat money.

Sure, some people do invest in Bitcoin and speculate, but because of
its superior properties, it is probably here to stay, and thus not just "a bubble".

Anyway, if you look at the 6 month price chart, there's no bubble shape.
It's been relatively flat in the $400-$600 range.