If you simply mine every other difficulty adjustment period you won't be taking advantage of the asymmetric difficulty adjustment. You'd just be sending a big pulse of mining power for one period when difficulty is low then going away the next one when it is high. You can do this on any blockchain out there. This happened to NameCoin earlier this summer before merged mining, lots of people left which caused a huge difficulty drop then everyone rushed back in and completed two weeks worth of blocks in less than two days.
You will if you have a large percent of the network, e.g. 50%. You will effectively mine at the same difficulty as if the network was only at half of the hash power. The algorithm SC2 uses for difficulty also increases block solvation exponentially with linear decreases in difficulty, so your return is much higher switching between difficulty periods.