Lurker, finally breaking cover....
Personal feel on BPMA is that associations/organisations of this kind justify their existence mostly through application of bulk buying power - the sort of 'member benefits' deals on cheaper insurance, discount on parts etc. That, I feel, is the basis on which many punters such as me for instance join owners clubs for specific types of car etc. - for the owners club insurance as much or more than the social opportunities (although they may be fun too). If however the benefits turn out to be so much vapour, the membership kind of shrivels quite soon down to the hard core of people who seem to get a buzz out of being on the letterheads of organisations....
There is also value in having a single pressure group to argue the member's viewpoint for example in the transponder situation - but to achieve anything it needs to avoid diluting the voice into too many different organisational voices (all insisting that they are the real Brian) and have credibility through numbers under its banner. For PG the BHPA has a presence recognised by the CAA due to a reasonable membership - but for many PG pilots I am sure that the main reason for staying with the BHPA at all is the 3rd party insurance that you buy as part of the annual subs. There is therefore a 'hard' reason for PG pilots to join/remain and therefore form part of the weight of numbers that keeps the BHPA voice audible.
Now if someone could combine some of the 'hard' advantages (saving a tenner here, a fiver there) with the positive "sod organisational politics, lets go flying" ethos of setups such as this forum (where new darksiders such as me can pick up a heck of a lot of useful information in an informal way) they'd be onto a winner for sure!
Dick G