HoudahSpot is more reliable than Spotlight at certain tasks, and can save standard searches.
Spotlight often doesn’t prove very good at finding certain items, such as tagged folders, even after you’ve forced it to rebuild its indexes by adding the volume to the Privacy list in the Spotlight pane, then removing it again. You can run a small suite of tests to confirm that Spotlight is working as intended using the free utility Mints from bit.ly/ml187mints, although that doesn’t test tags specifically, but text content.