Vroom's pretty good about announcing new features. For example, I used super search to locate nodes by him containing the word "new" in their titles and found his announcement rather quickly. Granted, it's near the bottom of the list (since super search orders by post date). A similar simple search returns the same link a little more quickly.
Constraining the same search to dates between January 1, 2001 and today reveals it even more quickly.
Also, certain helper elves have been known to post nodes outlining changes when Fearless forgets to. Consider, for example, this post.
Additionally, turnstep has been quietly maintaining his home node to outline new features, commonly asked questions, and (in)frequently posted suggestions. I've found that a very good summary of the broader changes to the Monastery. You might consider checking it out.
Finally, I'm not completely sure we want to full document all changes. For example, many things have been added in recent months to make life easier on vroom. For example, the janitors have been announced and given powers to help clean things up and limit trollish incursions. Documenting all of these changes could forewarn the trollish and lead to more inventive attacks. Dealing with these would take time away from our real mission: helping each other learn Perl.
I can see how this might help, of course, but given that we often encourage people to help themselves, it doesn't seem unreasonable to expect a little work on the part of the curious.
In short, it's not a bad idea, but we already have tools available for identifying new features designed to be publicized. I'm not necessarily disagreeing that it would be helpful, but I can think of other changes I'd like to see implemented first. (For two simple examples, see the following footnote.)
Footnote 1: It would certainly be nice to be able to 1) sort the results of Super Search and to 2) directly link to the results of a super search. Note that both ideas have been suggested before.