After some experimentation, it appears that the Twitter feed on my old site was at fault for the primary behavior that led to my ground-up reconstruction (administration issues). Perhaps some JavaScript variable naming conflicts were at issue. I have thus removed it, and although my site appears a little more bare, at least it works again. (I had also wanted to eliminate residual, unused database entries, so it's just as well—I've installed and then uninstalled quite a few modules over the past couple of years.)