Maybe I'm wrong about this, but... the difficulty level tells how hard it is to find a block; from this we can also calculate expected interval between finding blocks. But this assumes that the network hashrate remains constant since the last difficulty adjustment. In reality, the expected mining returns would trend more closely with network hashrate, especially if the hashrate increases significantly.
Correct?
Its the other way round. Difficulty is a number that determines what the odds are to find a block with a given hashrate. Average time in seconds is: difficulty * 2^32 / hashrate.
Difficulty is tuned so the entire network on average will find one block every 10 minutes. But if the overall network hashrate is bigger than before the previous adjustment, more blocks will be found than once every 10 minutes and so overall block generation time goes down, which will cause the next difficulty to rise. But your individual block generation time for your particular hashrate remains exactly the same until the difficulty changes.
Block generation time is currently 8.3 minutes (500 block avg), which will cause the next difficulty to go up by an estimated ~25-26%. As a result, your mining revenue per GH will drop proportionally and instantly once the new difficulty sets in. For petamine bag holders, that means your dividends will go down by an even larger fraction, since hosting fees dont scale with dividends. Oh and that 25% is on top of the previous 14.5% decrease which you havent felt yet.