Thing is, enforcement isn't necessarily going to move anyone to leave a review. If anything, it'll turn them off from reviewing completely. Reviews are meant to be what they're meant to be -- voluntary, out of the listener's ears and heart/mind.
Someone suggested in the Audio Adverts thread once that for every piece of audio we submit, we review five before us. Now granted, some of us are less versed in some genres (I wouldn't review hip-hop or dubstep, for example), but we can at least try to look back and tackle what we know, and if need be, look further back. I've taken up that idea ever since.
If everyone did this, then we'd have loads of reviews in no time.