I have been member for many, many years and have really enjoyed it and benefited from it. I would echo jim e's comments generally. I originally joined and became certified because of my then involvement with retail and tournament stringing--I actually do think it makes a difference in the retail stringing world (and I realize that there will always be folks that are content to let any kid with a machine string their racquets cheaply).
I have been out of the retail gig for a long time now and really pretty much only string for myself (and a few friends in a pinch) but I still play a ton (including many tournaments) and go through a great many strings. I remain a member for not only the great stringing manual and pattern book (of course I use the latter infrequently) but also to keep up on the latest tips and industry developments as well as the string and other samples. So, for me at least, I find membership enjoyable.
Ultimately, if you get really serious about stringing or just think you would like the extra resources/opportunities I would recommend it, if you have the cash to spare. Happy to answer any specific questions you may have. Good luck.