I'm a member of both, and I believe they are worth it. I joined the ECA because of the ability to purchase the newest runs of knives and request serial numbers before the general public. I haven't bought any special runs yet but the option was there. The Order of the Black Shamrock is only worth it if you believe in the ideals it stands for. I do, and I try to live my life by those ideals every day. If you are a fan of Emerson knives I suggest getting an ECA membership. If you believe in what the OBS stands for and want to be a positive member of a great organization, become a member of the OBS.
As far as the OBS knife, even for members it's extremely difficult to come by. Also, don't join the OBS just for a knife, that's not what it's about.