According to the current difficulty increase rate, to keep the same proportion (or dividend), it's not just adding 'some' hash rate. The hash rate has to be increase more than 30% every 10 days, and more than doubled per month. No company on earth can achieve this objective for one year. So 0.0005 - 0.0006 is definitely not the right price, unless you believe the network hashing rate will stop increasing exponentially in a couple of months.
If "no company on earth can achieve this objective" then actually the difficulty cannot continue to increase at this rate. Eventually every mining op will hit a wall, and what happens then is... the difficulty stops increasing at that rate.