Take a look at some of the upcoming events on the D23 website. If you able to attend any of those events, the membership might be worthwhile for you.
I wouldn't get the membership just for the magazine.
It also helps if you live near Disneyland or Disney World, because many of the events take place there....though they are trying to expand to other areas (San Francisco, Chicago, NYC).
We are not able to attend anything soon. We were there three weeks ago and are returning in October. I was wondering, besides the magazine, if there are any decent special lodging offers through this?