Don't believe that stuff about "electret effect". With a cylindrical conductor (the "shield") around the alleged "electret" (in the dilectric) the charge on the conductor creates the entire external field, regargless of the charge WITHIN the conductor.
Any amplification from "electrets" would have to come from something located OUTSIDE the collector cable. (And fields from electrets would quickly be canceled in a foggy or rainy environment by their selective attraction of charged raindrops which would coat them until their net charge at the surface was neutral.)
The increase in current, if any, compared to a simple wire comes from the larger diameter of the outer conductor of the shielded wire.
If you ground the inner conductor the dilectric also provides a large capacitance to help store charge from one discharge spike to another.
= = = =
You can use a trapped field to charge droplets, then the force of the wind to drive them to a similarly-charged collector. But the charged element providing the field will leak charge to other droplets and need constant refreshment.