Should you join? I'd say yes, but first I'd better mention a few things.
The EFDSS has had its share of troubles. I've been a member for 25 years, and have watched the "tea-dancers" seize control from what had been an encouragingly progressive executive committee, in order to preserve Cecil Sharp House as their own personal club, and a whole series of chief executives disappear in sometimes puzzling circumstances. Much of the problem has been an aging membership primarily concerned with social dancing and having little interest in music and none at all, in many cases, in the serious study of the traditional arts. For a good few years, the Library, the Journal and, to a lesser extent, the magazine often seemed to be the only really worthwhile things about the Society, and each of these had to be defended against attacks from members who had no interest in them and didn't see why they should have to pay anything toward their upkeep.
In short, a typical voluntary organisation! The English Folk Dance and Song Society is not about "controlling" anything; it aims to encourage, document and develop folk music, dance and song traditions within England, and has in the past done a great deal of valuable work to that end. It is far from perfect, but it is the only national organisation that we have. In recent years it has moved toward establishing partnerships with other organisations with overlapping remits; on the national level, the National Sound Archive; on the regional level, ventures such as Folkworks (run by professional musicians) and smaller, grassroots setups like the South Riding Folk Network. Publishing activities have resumed; on a relatively low-key basis so far, as the multi-media Root & Branch venture was not a commercial success, but there is more in the planning stages, including a project to make the Society's journals available online. The changes to English Dance and Song are part of a move to reach a much wider public.
There are considerable opportunities for the Society to make a go of current plans, but it's important that it attracts a lot more younger members (anybody under 60 would probably count as young at the moment) than has been the case over the last twenty years; this has required a fairly drastic re-think of internal structures, priorities and image, and it is inevitable that some of the membership won't like it. What the EFDSS needs is people who really believe in the folk arts; you don't have to be an active member (I haven't been for much of the time) but you can lend positive support just by joining. Though I live in Yorkshire and rarely have a chance to get to the Library, I've never felt, even at the height of the in-fighting of the late '80s, that my subscription was wasted.