If I wasn't selling at $5.99, I'd have scuttled my AA campaigns at this point.
Most of my ACoS are above 50% and I have one campaign, for Book II, that's above 100% that I'm keeping going because the CTR is like 1/130. I have a handful of campaigns that are at ~30% ACoS, but they've been around for a long time and a couple of them haven't generated a sale (or a click!) in months. (You all export your ads into Excel every 30 days and compare/contrast/analyze, right?) These non-movers are weird; it's like a few months ago they just went into stasis, or something. About the time, I reckon, that Amazon introduced Bid+.
One other thing that's hanging me up is that, looking at the last two months of AA since my sequel went live, ads for Book II in my series appear to be resulting in sales of Book I. Book I sales are way up, and clicks on Book II are better than clicks on Book I, although the ACoS on Book II ads are far higher across the board.
I think people are clicking on the AA for Book II, seeing that it's a sequel, and buying Book I, and when they eventually go back and buy Book II, it's not from a click-through so I'm not seeing it reflected in the ACoS even though I effectively made two sales out of that click. I say this because the Book II ACoS is out of hand for nearly every campaign, but the ads as a percentage of monthly income are staying reasonable. For this reason, I'm continuing to run the ad for Book II that has the killer CTR even though the ACoS is over 100%.
ETA: All that said, looking at my numbers and doing some quick math, if I was selling at $2.99 or even $3.99, AA wouldn't be sustainable.