Michael,
I've made a truck load of half baked decisions, most of my mistakes are behind me now 
. Some thoughts I'd like to pass on to you:
1st question: How Are you paid? Sales commission or cost savings or salary? I don't expect you to tell us, but I ask this because it influences how you look at the world. I was paid by commission from sales of the entire org, so it was my job to help the owner manage the multi-million dollar marketing spend and push the owner into advertising that brought the biggest commission check I could make. My pay plan aligned with the owners
Your write:
IMO, this is a serious warning sign. I'd like to know "Why nothing happened when I shut off traffic to my site?" You have to do detective work. Is PPC a waste of money, or, was the PPC campaign a P.O.S.? Are my website pages at fault? Are my measurements looking for success measuring the wrong things? If it were me, I'd be comparing engagement metrics of long tail SEO vs long tail PPC.
You write:
You've connected Increasing traffic & referrals to dropping PPC ads. I'd bet is related to seasonality or Chevy's marketing, or a competitor's marketing and/or ChevyLand's marketing.
You write:
I'm puzzled. Did you mean to say:
"I think the money spent on ppc I would have gotten organically. Can you see this in google analytics?" That's what I'm trying to find out.
Yes, you can see that in GA. Look back and find your top20 PPC long tail phrases and see how much duplicate organic SEO traffic you had. Now fast forward into today and see what the impact looks like (note: include your SEO gaps where PPC traffic had zero SEO traffic).
Lastly, I'd take that same list and see how "productive" that traffic was relative to your website. How likely was this long tail PPC shopper to look at more than one car? How likely was he to return (at NO charge .
HTH
Joe
