There are many people whom enjoy hearing new songs which makes Spotify great! Some users may only remember the chorus or a couple of phrases. Include a text field in Spotify (similar to the forum compose box) that will allow people to search type lyrics. Maybe up to 500 characters if there are backend limitations.
Hi, a similar idea has also been suggested here:
Add your kudos and comments there please! You might also note that MusiXmatch possesses this funcitonality.