The LAA is unquestionably a force for good as far as light and grass roots aviation goes. The magazine is the only light GA magazine that is worth reading (that I've known of) beyond that first year of reading pilot and it's full of help and assistance for those who want to know more.
I have no doubt that the coaching scheme is also well run on the basis of a couple of small exchanges that I've had with the guy that runs it. I chose not to go further, I'm flying away for work most of my days so home time is used exclusively for family and my own wee machine. That said when I get the opportunity to have some more time I really very much want to be part of it because I enjoy it and I don't think it's something you can easily get in all parts of the country from the flying schools available.
I didn't think you actually needed to be an owner/part owner to be a member of the LAA, you just needed to pay your membership. The magazine alone makes it worth it. Even so unless you're serious about touring by IFR I can't think of any reason to fly EASA CofA aircraft.
If you want to know more, head for Sywell at the end of the month.