Yep, my opening disclaimer is that it is based on the musician..but now--in my opinion:

I am a music guy. Lyrics are important (sometimes), but not the integral part of the song.

If someone is lyrics only--and they hear the tune in their head--there is no excuse not to get to a piano or kbd and plink around until you find the notes to atleast flesh out crudely that tune in your head. If you don't "hear" the tune and it really is lyrics only,..what else is there to say. It may be a song, it may be a poem...but there isn't a song until there is music.