Well I think part of the reason that we are stay at 14.00 USD is because of this fee. Honestly I would keep it at 0.1 for now. In few weeks it will go back up. Also, just browsing through the forums a lot of people are taking a break from mining do to this summer heat. I believe that once we get later in the year when all these power machines start outputting heat to heat our homes, more people will jump online and fee's will go up.
It's basically a trend.
I've never thought about that, but your right. It's also demand, since people aren't mining in the summer, there won't be as many people generating coins... meaning the price will rise when people will need it.
Doesn't matter how many people mine, there will still be an average of 6 blocks an hour generated, the difficulty will just go down if people really do leave.