Well it's very impressive that you got that performance without using any dual-pol parameters. Abstract submission for the AMS radar conference is next week, and I'm sure they'd be interested in this. http://www.ametsoc.org/MEET/fainst/201336radar.html

Also, correct me if I'm wrong (and I very well could be), but the most egregious noise -- the giant Bagel Blobs -- aren't insect reflections, but rather night-time temperature inversions. Can dual-pol correlation help identify those?

It's likely a combination of both. A quick way to discern would be to look at velocity, zdr, and rhohv. For ground clutter and returns caused by the inversion, you will expect to see very low velocities(close to 0) relative to the background precipitation. Additionally Zdr will end up looking like a roughly random field. If it is insects, then the velocity will roughly match the background precipitation, but you will have a high zdr(as insects look like very very oblate bags of water). In both cases you should get a drop in rho_hv, the correlation coefficient between the channels which will help to differentiate it from actual precipitation. Also it looks like you're primarily concerned with pulling out the rainfall in several cases. For this, I'd look at the specific differential phase(K_DP) as it is a much better estimator of rainfall than reflectivity. In general, it is linearly proportional(exponential, with an exponent close to 1) to the rainfall rate. I'm not sure how good the nexrad estimators are for kdp though.