i love your idea. no sarcasm here. that's exactly what i do with my punk songs (and my attempts at technical metal). i always get the chords, the rhythm and the theme(heavy/soft,dark-sounding/light-hearted) before lyrics get it there.
also, as Josh Redstone said previously, if it sounds good without lyrics then it's a good song. i normally play my songs for about 15-20 minutes over and over without lyrics (i normally don't have any then)and then words fall into place.
keep it up you guys.
Thanks for listening to this small piece of me.