It did need replacing. Badly. Wow. It's a five-micron filter, so it filters out pretty much everything from sediment to fat bacteria, and I think it was last replaced in 2004 or so, it was pretty full of gook.
Now I have water pressure again.
Someday I may add a reverse-osmosis filter for drinky water, and I'd love to add a UV exposure filter to destroy any living organisms, but really that's pretty overkill-ish.