I've been a lucid/very lucid/very,very lucid dreamer for over ten years now and quite frankly, I still don't know what the hell is going on. I've gone through many books to see if I could find someone else who'd either had the same experiences or who knew something of them. To date I've not been satisfied.
I've never seen a silver cord, and believe you me I've been up up and away. I'm also a little unsettled with this notion of bad spirits hanging around waiting to do bad things to us. I've had a few negative experiences but I think it's important to maintain the puzzle. A few pieces here and there does not make a complete picture. And so there with a few not so lovely lucid dreams I've had some extremely beautiful ones. That's why I go. I don't know how it happens but I can usually feel it right before it does. I dont try. I just let go. And one more thing. I think it's helpful if your searching for something. My need to know and understand what love truly is has been the one and only motivating force. You'll stand up to anything for it.
The silver chord is usually seen in realtime-zone astral projection. Lucid dreaming is more of personal inner experience.
I've seen the chord while OBE, but it was a faint luminous green rather than silver in my perception.
Regarding negative experiences. In the LD realms these could be seen more as inner fears or repressed negative emotion/archtypes. One thing to always keep in mind is that nothing can truely harm you.
Oz? I hope you mean the books and not that awful prison show. Have you read them? I downloaded a couple (some are public domain now), and intend to read them soon, it's so romantic.