Me too... I am down 40%. I used to get traffic on over 7,000 keywords monthly. A have a 500 page website so the usually jargon about "build quality content and you are safe" is a failed strategy.
I think you have to look deeper at Google's big picture strategy (its ugly).
Every time there is a major change in the search algorithm they make all prior SEO work nearly worthless.
Why would Google do that?
Three reasons:
1. They think they own the internet. They have been muscling in on organic search results for years. They now give Google products more and more space on landing pages and using Google maps is a take over of the internet. Do you have any doubt that they will eventually charge for Google maps and thus eliminate the need for a great portion of organic content. Isn't it amazing that they prohibit "link building schemes" yet that is where they get all of their profits i.e., Adwords. The internet was created to be a public resource utility. It's a Google owned corporate asset now and to a great extent they control the value of everyone's website.
2. Google has hijacked the internet. When they reshuffle the search results they create a lot of new losers who need to buy Adwods to recoup traffic. But note, there are not an equal amount of new winners. Many of the top rank positions in my niche are from (sterile) government sites and Wikipedia. (they don't buy Adwords) Neither do they pick up the phone and give people personal advice 24/7 (like I used to).
3. Big brand companies have been pressuring Google for years. Big companies want the little guy out of the internet and with every algorithm they get closer to their goal. Smaller companies don't have the resources to "start over" every 12 months, big companies do.
Frankly, I think it is over for the SEO business. (that's the way Google wants it) How can someone charge people a reasonable fee when Google can shuffle the deck anytime they want and make that work worthless?
It's become an anti-trust issue they need new competitors and consumers need choices. I liked the old search results better... but I don't have the choice and neither does anyone else. I also want to opt out of Adwords and local maps too. Their billion dollar link building schemes is a violation of my SEO policy.
Looking for a new line of work... another attack on the little guy. (it's Pottersville on a global scale)
Good luck..
Bri