An interesting addition to the data dump would be the daily/hourly/whatever view counts for the websites. This could be used to see what happened to SO when proposal X came out, what time of day is the most active (if it was hourly), what day of the week is the most active, activity to question ratio, and many other things.
Before you say "What about
Posts.ViewCount?", they aren't usable since they only list the total, not the breakdown of when it happened. The only statistics you could draw are monthly, which is useless.
If your worried about size, then your exaggerating what I'm asking. Daily is tiny, only 7 rows for an entire week. Hourly is a bit bigger, 168 rows per week. Considering other tables are millions of rows long, this won't affect size at all considering the growth.