The magnitude drop you are experiencing is indeed increased competition. Over the last 5 days we have seen almost 100 new CPIDs register with the network, and the rate of growth is still going up. GRC 'mining' is never going to be as easy again as it is now - and that will result in a price rise!
Keep crunching. =)
If we add the users who joined the pool without creating an own CPID it's even more :)
That is a really good point I did not even think about. The pool is getting utterly massive!