Ramsey on diaries vs. PPM, from the ad buyer's POV

On his blog, media strategist Mark Ramsey argues that the old Arbitron diaries were better at showing which stations a listener actually values and engages with, as opposed to PPM, which doesn’t depend on a listener’s impressions to record and deliver data. Check out his video.

If Ramsey is right, what are the implications for public radio? Are stations that have abandoned diaries missing out on valuable information, and, if so, how to recover it?