Bitcoin
Bank Wire:
~$45 per transaction
That is very much a worst case number. US domestic, and I believe SEPA, bank wires are half that. Cash deposits range from zero to a few percent using a service.
I do grant the convenience factor. Credit cards "just work", for a known percentage. Bank wires and cash deposits are more work with unpredictable delays.
I agree with the OP that the requirement for mass adoption is vendors selling for Bitcoin being able to spend the Bitcoin on rather than having to convert it back to fiat.
Yes, in this sense it is kind of stuck in a self-sustaining loop. Basically we need merchants to get Bitcoin more widely adopted, but we'll only get more merchants when the Bitcoin price is stable. And this will if course only happen when more people use Bitcoin. Which only happens when we have more merchants. Repeat ad infinitum.
I think that we'll really see the Bitcoin become stable when actually producing stuff can be done in Bitcoin. i.e., If you want to sell bread for Bitcoin, it is much more viable if you can buy the wheat and eggs you need to create it in Bitcoin as well, as this means that the price of the product doesn't need to fluctuate with the exchange rates of another currency.
the Avalon ASIC is one of the first devices that I know of that seems to work that way.