Definately both.
When Im listening to a new album I want to read along with lyrics to really get an insight to what the lyricist is trying to portray.
Of course this is only with a range of artist. If Im listening to new Metal/Grind album Im not going to care much for the lyrics as long as they aren't ridiculous, as the genre is more about the instrumentation (In my opinion).
Listening to a new Emo/Indie/Melodic Hardcore record is best done witht he lyrics in front of you. A briliant example being Touche Amore's new album. I preordered the LP and when it arrived put it straight on the turntable, pulled out the lyrics insert and listened to it front to back twice over. That album and that band wouldn't be the same without Jeremys brilliant songwriting ability.
I think popular music is more about the 'catchy tune' of the song, thats what gets it radio play. Lyrics in Pop music today (and I guess throughout the age of Pop music) is full of cringe worthy, generic verses and stupid 'catchy' choruses. All Pop music isnt like this but Id say at least 95% of it is. Look at songs like 'Starships' by Nicki Minaj. Read the lyrics
HERE and you'll understand what I mean.
Some songs just wouldn't be the same without their 'catchy tune'.
I guess with most of the music I listen to the lyrics are just as important as the song itself. Its the perfect combination of the two that makes a good songs.
To answer your question;
Lyrics are just as important as the instrumentation in a song. Without half decent lyrics a song lacks not only talent, but heart.
Many of the bands I have listened to have really shaped my outlook on life and molded me into a person I wasn't before (In a positive way I believe). So I will say that music, that being the music along with its lyrics, have changed my life.