I think that the difference between instrumental and vocal (meaning lyric-based) music is a strength and a weakness for both sides. Using words allows you to say things more specifically, thing that you can't say with sound alone; using sound lets you communicate more broadly with feelings and atmospheres. Of course most pop music does both of these - vocals + accompinament is the standard form. However, in my opinion the huge majority of lyrics going around mainstream music at the moment are really a cop out, borrowed/ stolen or altered generic phrases that let you show off your chops. If you don't have anything concrete to say, just make some syllables up. That's scat singing. Words are very dangerous and precious things, and we need to be careful not to waste them.
Tom Waits may not be the most ingenious or beautiful or anything lyricist in the world, but what he does is respect our language. He sings his lyrics how they need to be sung - if that means talking a verse then he will talk a verse. He uses a huge range of voices to convey the mood and story of his songs. If you turn on Whoever's Got Talent you will see the opposite - good (technically proficient) singers using words as a vehicle to be virtuosic. Nothing wrong with being a virtuoso, but if you want to tell a story you have to sing it like it's a story. Another example of someone who is a story teller first and a singer second is Nick Cave - he doesn't do a lot with his voice, but when he does do something, you know about it and it is effective.
Any fans of a story, get Tom Waits' Rain Dogs.
