Tony,
I don't know about page vandalism, but I do know that the navigation structure of the site was messed with by Ævar Arnfjörð Bjarmason, Fennec, and Pakaran. Such changes can easily make the site effectively unusable for newbies.
I ask you not to dismiss concerns about this matter too easily as "boring people not getting it." The very real problem here is that on an openly editable site, everyone seems to feel they have license to make their own little joke, and the accumulation of all of them together is a little too much. A lot of serious magazines and newspapers have an April Fool's joke, but very few have more than one.
As an educational resource, we have a responsibility to maintain the integrity and the accessibility of our information. People should feel that they are visiting a site run by people with a sense of humor, but it shouldn't look like a site run by drunk teenagers either.
As such, I propose two simple rules for next year:
1) There will be one well-coordinated joke for the *outside* world, Whether it's a featured article, a press release, or anything else can be decided by the cabal on the to-be-created fools-l@wikimedia.org mailing list ;-).
2) Jokes *within* the community are limited to the Wikipedia:, User: and *Talk: namespaces. MediaWiki:, Template:, Image: and articles are off limits. Jokes should not be overly disruptive.
There's still plenty of room for spontaneity, but sanity and integrity to the outside world are preserved.
Erik