diberry - 2:49 pm on Apr 27, 2013 (gmt 0)
This sounds like your new traffic (the increase) is not as well targeted as the original traffic was.
Have your rankings in Google gotten better? If so, the spammers always follow that trail to see if you've got anything they can use. So a Google ranking will not only increase your Google traffic - which in itself may or may not be well-optimized - but traffic from all kinds of other sources, which is actually just spam/bots/SEO stuff.