I'm just starting my dream journal myself. But I've had two dreams in the past year that I will probably never forget, just because of how vivid they were while having them. Heck, I may have been in a lucid state during them and didn't know it. For me personally, I find that vivid dreams are really important for finding dream signs, as long as you can remember very specific details within them. But then again, if you couldn't, why would you call them a vivid dream?