This conversation has been merged. Please reference the main conversation: Lightroom: A better search/find in the library module (Library Filter)
Rob Cole's plugin DevMeta comes close to providing this ability, but because it relies on image selection to update it's private cache of Lightroom metadata the results are often out of date. I don't blame this on RC's plugin, but rather the fact that Lightroom doesn't expose this information in the Metadata Filtering functionality. To provide a balance between functionality and performance RC's plugin doesn't extract more nuanced information such as tone curve region parameters or individual curve modifications.
In addition, because the API doesn't allow for sufficiently rich metadata comparisons (contains, start and end) it's impossible to adequately work with this expanded metadata.
At a minimum, everything that RC's DevMeta plugin does should be standard in Lightroom. Metadata comparisons must support numeric, boolean, negation and range comparisons. It would be a bonus if word, list, and regex comparisons were also available.