*A <ref/> tag with no body anywhere in the
article should have some sort
of glaring red warning to that effect, in the same sort of manner as we
see when a <math> tag is fed badly formatted TeX. The current system
produces a blank reference, which is better than nothing but still kind
of easy to overlook.
*A <ref> tag whose body is defined but not actually used anywhere in the
article should still appear in the <references/>-generated list, with a
bullet instead of a number. This is already done manually in a lot of
cases when people add references directly to the references section.
Both good ideas.