Should writers join organizations like SCBWI or LDStorymakers?
You don't have to, but yes, I think you should. And RWA, and SFWA, and MWA, and LUW (or your state's equivalent), and Latter-day Authors, and other writer groups and forums, and reader groups and forums, and...
There are all sorts of groups out there that provide wonderful information, networking opportunities and support. Don't join them all or you'll spread yourself too thin and never have time to actually write. And don't join any that are out of your budget. But check into some of them and find one or two that fit your needs.
Readers, which organizations have you found to be most helpful?