Spotlight (and Finder) search on a ton of different things: name, size, dates, metadata in the file such as f-stop , aperture, etc for images, various audio data for audio files, the list goes on.
One thing you can do is add tags or descriptions to the comments field. Select a file in Finder and do File->Get Info. You can add and edit in the comments field and then use what you put in there when you search.
It will if you search for the tags. If for example you label all documents that have to do with your TV with the comment TV and you searched for all files with TV in the comments it would find those files.
You're right it can be time consuming especially if you try to go back and tag files that are already on the filesystem. If you do it going forward it's not to bad but does require discipline.