Thanks for the responses.
I do use a phono preamp. I can't entirely discount the possibility that my input levels are too low, though I've tried to compensate for that. I've tried recording the output of a variety of devices (LP's, cassettes, and minidiscs) with different software and had the impression that they all seemed a bit low even with the recording levels set high (a property of my SB Live soundcard's aux in?), though the overall quality was quite satisfactory.
I find that the MJ auto volume level control goes all over the place (60%-95%) even on repeated trials on the same section of music. I've currently set the volume at about 70% because when the autovolume control stayed much higher it would subsequently warn about distortion. Also, recording at that level, if I later use the Media Editor to normalize the volume level to, say, 95%, there's actually not a very dramatic change in volume, which I took as an indicator that I'm already somewhere in that neighborhood.
I'll give it a try at higher levels, listening for distortion "by ear".
I still wonder, though, whether it would not be a useful option to split tracks without entering the "waiting for sound" process. When recording from most sources, the inter-track gap isn't really that large that it would be distracting if it were preserved (and I suspect that, if the tracks were trimmed of all that separating material, I would then wind up burning my CD's with the "insert silence between tracks" box checked).