Howard:
Agreed.
In terms of the reporting of what's played, it's long been the case AFAIK that people can report it. With membership being £10, there's the opportunity to work within the existing framework at very little expense in terms of time or money, through the small gigs and bars. It might require the host to make notes sometimes (not _all_ the time - so not exhaustive, but representative) and copy and paste into an excel spreadhseet to send off every 6 months/year.
There are special rates for not-for-profits, but since the typical session (however community-music-making it may be) occurs in a pub, it's easy to see why these don't apply. The fee for spontaneous music-making (don't ask me for a definition, ask them..) is much less than a standard live-music fee - about £3 IIRC.

As far as your contention that it "does not own the rights to much of the music being performed", that's clearly a potential issue; in practice the content of sessions is as multifarious as the participants themselves, and gig situations are also varied, and the range of licences the PRS administers attempts to reflect that.

It's all bureaucracy for the profit-maker of course, which is to be lamented, but we insist they put people serving drinks on payrolls with minimum wages and I'm sure there are some who moan about that too.

Cheers

Dan Plews