That's a difficult one. You're certainly not alone in questioning the value of local associations, especially for small parish councils that rarely, if ever, make use of their services. My local association is, effectively, a single person and, for a variety of reasons, he has been unavailable to us for a large part of the past year.
I have heard stories of groups of parishes sharing a single membership to reduce the cost, unofficially, of course, or clerks who cover a number of parishes rotating a membership between them over a period of years. This is more relevant in the case of one-off advice than attending training courses etc.