Adoption and usage is most definitely related to the value, though, at least in the long term. Remember how Silk Road picked up in May? And of course it influences the value also because speculators gain more confidence as they see adoption increase. If they see the opposite, like from June to December, price will decrease.
Or do you think a market cap of barely 40 million will satisfy a "mainstream" currency?
I could be naive in this, but to me, mainstream is when you see people using bitcoin on the streets.
It doesn't matter if they use it once a month, for $1 a day only, all that matters is that they're using it.
I have heard the ex-forex trading initiative here speak so verbosely about how the value of Bitcoin is directly related to the USD put into it, but that's just simply not true. If there are 1000 people willing to trade 1 BTC, then that 1000 people are the ones who set the value. Exchanges are the friend of Bitcoin's adoption and the enemy of its stability.
EDIT: since there are many things about trading that are not my cup of tea, I don't want to pollute this thread with my lack of education on the matters. If we discuss this any deeper, let's start a new thread.