If you had it index everything you want to find it would do just that. And be excruciatingly slow, unreliable and wasting Gigabytes of storage. All while consuming tons of CPU time in the background.

The idea of an indexing service is good though. KDE's Baloo faces similar issues. It's not that easy to make it a good experience.

Everything (mentioned in this thread) comes closest to being fast, reliable, and usable. It can even index external disks and search them while offline.

Yet spotlight did manage to do just that without those drawbacks.

For some reason its accuracy has dropped in recent years but in the Tiger days it was really good.