I disagree. For a low traffic site, its probably performant enough with just APC caching, which the installer sets up for you. Vanilla mediawiki does the things you expect a wiki to do. I doubt these types of users want/need complex things like abuse filter and lua. (Unless you are copying templates from wikipedia)
The major thing out of the box mw is missing is confirm edit. The other stuff is cool but non-essential imo.
Just want to throw in my hat here as well. I use Mediawiki on my personal website, my laptop, and my place of business. In each case it fulfils a different role. In the case of my laptop, I don't need caching it just acts a good place to take notes on a variety of projects that I working on. I went with it because I was used to how it worked from editing Wikipedia and it was easy to set up. My laptop runs Windows with a copy of Apache and PHP installed on it for development work.
On my personal website I have a wiki that requires an account to edit with account creation disabled. I don’t use caching their either, but if my site got more traffic I would. In this case I installed Mediawiki in order to be able to quickly create pages of text for documentation or when translating news articles for people for political advocacy. On my personal website Mediawiki is set up on a shared host with all of the disadvantages that come with such a setup.
At my work we use Mediawiki as a knowledge base and to document standard operating procedures. Here Mediawiki was chosen for its ease of use for an end user and the audit trail that articles inherently leave. It was a bonus that I have experience writing Mediawiki extensions as well. Here we run it on a dedicated web server running Ubuntu Server Edition that I have root on.
Anyhow, I guess I didn't really make what I'm trying to say here terribly clear. Lots of people use Mediawiki for a lot of different reasons in a lot of different enviornments. I can't easily set up many of the items that are used by the WMF on my Windows laptop, nor on my shared hosting account. Personally in those situations I would enjoy Mediawiki to still work reasonably well.
By all means drop the file cache if no one really uses it, but I personally would be against dropping support for people who are in shared hosting environments or other environment that don't match up with the typical VPS or dedicated server.
Thank you, Derric Atzrott
...now back to lurking.