Honestly the best thing I ever did was release some of my stash. I had a friend come over and we went through the entire room and pulled out everything hidden.
My friend would hold up an item, "what is this? what do you plan to do with it? why do you have it?"
If I didn't have a ready answer it went into the donation pile. She helped me put my room back together and kept chanting "everything has it's place" It was very nice for a few weeks. Now it's bad, but no where near as bad as it was in the beginning. I"m slightly more organized, my thread is all in one container, blades and anything sharp in another.
So go ahead and fling selectively. If you have supplies for crafts that you no longer enjoy doing, fabric from the '70's, silky stuff from dress making attempts that you don't plan to use, find a good charity and donate.