Thanks for the input, everybody - I appreciate it. Jomi - if anything, I considered pushing the vocals even further back in the mix!
I thought they were the weakest part of the song by far - I literally wrote the lyrics in about 10 minutes, and by the time I got to laying the vocal track I had spent most of the day on the drums and all the guitar tracks - I treated the vox almost as an afterthought. I really should have re-done them (and I will at some point), but I got in a hurry to finish the song. I wouldn't go quite so far as to say they were a "scratch track", but it's not too far from the truth.