Spotlight was showing fewer and fewer results until one day it stopped even showing results from /Applications. As this is how I launch apps, something had to be done!
Opening up Terminal.app:
$ sudo mdutil -i on -E / /: Error: unable to perform operation. (-400) No index.
OK, so I need to delete the index, kill all the associated processes and hopefully things will restart.
$ sudo rm -rf /.Spotlight-V100/ $ sudo killall -9 mdworker $ sudo killall -9 mds $ sudo mdutil -i on -E / /: Indexing enabled.
Presto! Everything working again as normal!