MediaWiki captchas are terrible and literally worse than useless (keep many humans out, fail to keep spambots out). reCaptcha is a little less worse. But if they have something that works for wiki spam, please be sure to post it to mediawiki-l! Thank you :-)
Protecting one specific Wiki from spam and protecting Wiki's in general from spam are two different problems. Spam security by obscurity works for a single Wiki.
It seems that if you look at the column on the right of the page, you can see upvotes and downvotes separately for recent posts. The same [n, m] format is displayed for recent comments, but it doesn't seem to actually sync with the score displaying on the comment. This feature only seems available on the sidebar: looking at the actual comment or post doesn't give you this information.
Thanks, whoever did this!