My original sample was a 100K sample from zero-results queries to enwiki on 7/24. Today I looked at similar samples from 7/10 and 7/17 (since there is a weekly pattern to traffic) and from 7/22 to compare.
All of the patterns I detected are still present, in approximately the same volume (give or take a factor of 2), except for the ('"<TITLE>"', '<AUTHOR(S)>') pattern.
I've started looking at a 500K sample from 7/24 across all wikis. I'll have more results tomorrow, but right now it's already clear that someone is spamming useless DOI searches across wikis—and it's 9% of the wiki zero-results queries.
—Trey