we are pretty unhappy about the skimpy upgrade documentation
Hmm, true, but are you volunteering to help write better documentation? (General principle in FOSS: If you don't like it, volunteer to help if you're able.)
At least this time there is an UPGRADE document. That never happened before in any other release, which is a small step forward. Prior releases got a few terse notes about the major issues added to README, but nothing nearly as in-depth as the still-sparse UPGRADE document from 3.0.
and the number of apparently-gratuitous changes ("hits" becomes "score"?).
You'd not believe the number of people who don't understand what SA means by "hits" when they first encounter it. Particularly since SA used to use "score" "hits" and "points" interchangeably and without much consistency.
A lot of naming convention changes come about after realizing that the original naming isn't as clear as originally thought, or inconsistent with other parts of the software. It's painful to go through, but makes life a bit easier on the project in the long run by improving clarity.
This lack of consistency has been in the buglist for a long time.
http://bugzilla.spamassassin.org/show_bug.cgi?id=1332
