I love being a PTA member and I think it's fairly well appreciated in our school. Sometimes we could do with a bit more of the T in the PTFA, but it's got better recently. I do understand how busy teachers are though. It is dispiriting when parents come along to meetings just for a moan at (quite minor IMHO) things about the school- I tell them to go to a Governor's surgery :). I suppose it could be seen as quite cliquey, but we try to communicate well with parents - Parentmail, facebook, school website, letters, face to face, school blackboard/noticeboard. And we get new parents every year coming along to meetings or joining the committee.
Though we seem to get the same faces and at times have trouble convincing people to help out at times generally, financially we do quite well and don't have trouble getting cakes/bottles/sweets/money from parents. I think some parents don't help out as a lot of people aren't confident enough to put themselves outside their comfort zone, or think it will take more time than they imagine, or that they will get roped in to more than they can manage, or feel they have just too many other things going on, which I can understand perfectly. Very few, I think, don't care.
Recently we have helped fund quite a large project at the school which will provide lasting, visible benefit for pupils so I think what we do has been reinforced. We have a new headteacher starting in Sept who seems very supportive, so I'm optimistic.
For me personally, though organising events can be hard work, I find it so absorbing it kind of helps me manage stress from work - I totally switch off from work and think about what I'm doing. My parents were never involved with the school and were never there as they both worked. Looking back I always felt 'on my own' at school, being an only child too, most kids had siblings or parents around. That's where my motivation comes from, I may work (practically) fully time but if I get to know other parents through helping out I think it helps my DDs feel more supported at school.
DH has just become a Governor as well, so I do feel particularly sharp-elbowed! I would encourage anyone to be involved how you can though, particularly say, SAHPs who have been out of the workplace for a number of years, it could give you the confidence and experience to be able to get a job if you wanted to, or open up opportunities you never imagined. It has for me, and I am still working. Also you can put into place the skills you gained through working, our Treasurer used to be an accountant, for example.