The most important consequence of bitcoin is watching programmers and other tech oriented people play armchair economist. They certainly seem to be having lots of fun but they are playing a game no economist recognizes.
That's an unfair criticism, since the arguments I address are exactly those raised by everyone else who has written on the subject.
What you actually seem to be addressing is whether the statement "Bitcoin cannot work as a medium of exchange" is true.
I'm not sold on your second point "someone who sells a Bitcoin for X would have been equally happy to spend it on something they value at X." Using daily volume on Gox as an example, just because $2M changed hands yesterday, it doesn't necessarily imply that these folks would have happily exchange their coins for a good or service. A lot of this volume could represent traders getting in and out of a position, not someone ready to empty their account. However, your general point is that liquidity is a positive reinforcing signal, and I can agree with that. If liquidity is increasing because more merchants need to swap out, this is a direct indication that spenders are willing to transact.