Are miners currently a large enough portion of people selling bitcoins to significantly impact their price?
3600 bitcoins are mined every day. About 50,000 BTC are traded every day. If every bitcoin that was mined was sold on on an exchange, those sales would only account for about 7% of the total exchange volume.
The fact that mined bitcoins are a small part of exchange volume and that there is no mining cartel, leads me to believe that the actions of miners have no effect on the price of BTC.
Your numbers are incorrect because the 50.000 BTC traded every day include transactions happening from the same person at that day.
For example one buys at X price, then when price is y he sells. Then decides to buy again when price is Z and then sells.....
The TOTAL of those transactions is the number of coins traded each day.
For example that person can start with 100BTC keep on selling and buying all day and still have 100BTC at the end of the day, while the amount of "traded" BTC will be much higher that 100BTC.
So i believe the amount of bitcoins mined account to a much higher number of real daily trades.