Hi Mike
It's quite difficult to say, but I would offer this bit of solace: When I've seen sites that have been hit with a Panda penalty in the past, it has happened a day or 2 after receiving a similar warning to the one you have reported.
And similarly, although not the same penalty, people have reported that they have received an unnatural link warning and then 2 or 3 days later have seen the big drop in rankings and traffic.
Both of these instances indicate that the notification of a possibly penalty comes before the penalty itself. If (and it is an 'if') this is the case with your site, then the big drop in traffic can be attributed to the penalty that you thought was coming, rather than the action you took yourself.
It does sound like the crawl and the warning would result in potential duplicate content issues or low quality content issues, aka a Panda penalty. I'd take out due diligence and make sure that you have not blocked any key landing pages via robots.txt file or by any other method - always a good idea to double check. However, if that's not the case, I would say that the drop is because of the penalty that was likely coming, rather than what you've done.
The next step would be to wait until the algorithm refreshes - Panda updates rollout at least twice a month now so hopefully your efforts should be rewarded soon enough and the traffic will return.
However, it is worth considering that just because the Penguin algorithm updates on a given day, does not mean its impacted is limited to the day or the days that follow. What I think we've seen with Penguin 2.0 is the impact of the algorithm updating has been spread out over refreshes, so we can't completely rule out this as Penguin action as well. SERP volatility checkers like Mozcast seem to suggest that this probably isn't the case, all was quiet on August 13th on that algorithm, but it's worth bearing in mind.
I hope this helps - do take my advice with a pinch of salt as it's an educated guess from my experience rather than any definitive evidence.