Here in .nz the national library runs a local aggregation service
http://digitalnz.org/ which has quite good penetration into schools
and so forth. It provides some metadata quality reports such as
http://metadata.digitalnz.org/nzresearch/127 for sources it aggregates
(that report is actually quite a bit dated).
My experience of these reports is they're useful in inverse proportion
to the diversity of the collection being reported on. The narrower
your collection, the more real issues are going to be caught.
...let us be heard from red core to black sky