I think it's a good idea, and I agree with Saka about identifiable OP/ED. There are too much BGM that can be glossed over in series, and I'm afraid of the Yoko Kanno flood (although I wouldn't mind listening to her works). Although the OP/ED consists of Jpop, at the same time most people who watch these series have heard it 26 times through (unless they skip it) or have downloaded it. However a drawback to an OP/ED only contest is that there are unoriginal tracks like Franz Ferdinand's Do You Want To? (Paradise Kiss ED). Although the band is greatness themselves, we can't nominate songs like that, in my opinion.
One of the things I'm afraid of myself is nominating not so new series, simply because I'm not up to date with anime as I used to.
Jam it back in, in the dark.