And there's the answer

In comments here, pogge notes that at least some of the Cons' publicly-funded ten-per-centers have served to drive traffic directly to partisan websites:

The last couple of ten percenters I've received from my Conservative MP have encouraged me to provide my feedback by filling out an online survey -- at the Conservative Party website. I checked one out and discovered that name, mailing address and email address were required in order to submit my answer to the single survey question. It's just another way of using a taxpayer funded mailing to build a Conservative Party database.

So while there's plenty more to be discovered about exactly what the Cons have done with the material they've received by mail, there doesn't seem to be any room for doubt that some information derived from Con MPs' publicly-funded mailers has been entirely for the benefit of the Conservative Party rather than having any pretense of trying to listen to constituents.

Meanwhile, burlivespipe has an excellent suggestion as to how to respond in order to thoroughly smoke out the Cons' misuse of public resources:

Next time I get one instead of recycling it, or as I've occasionally done, sent back with a snide comment, I am going to put down some faint praise and my info. It would be a privilege to see if this does 'track-back' in terms of a financial plea... That would make a pretty impressive post and possible legitimate news story.