I left it a little longer than a week, during which time I didn’t change any of the blogs, add or edit any posts, or even check the search results.
Today, the home page of the site is back up to #9 for the search term “search experiments”, which makes the previous change look something like the usual non-random churn.
Could it be that the initial dip was some kind of penalty, but the fact that no new splog posts have been published means that the penalty has diminished? It could, but there are a hundred other possible explanations. Beware of jumping to conclusions.