I worked as a technical writer earlier in this century and was a member of the STC for a year. In my case, that was a year too long. Like more than a few other technical writers I knew and worked with, I didn't get any value out of my membership. I got more out of the (at the time) burgeoning technical communication blogosphere than I did from the STC

The STC, at least in my view, was several steps behind the times. It was a large organization that was too slow to adapt to changing realities.