Well, it is flat here, and I don't ride the really tuff stuff like that. But when I've been caught out after dark, I've been amazed to realize that I've wandered through stuff I would never in a zillion years try if I knew I was on it- a really good fork is a blessing. It lets you feel the ground but eats the dangerous stuff. And sometimes you get a few amazing experiences in life- but only the few. My gut says get a light, don't push it.
Night vision is a learned skill- I dated an ex Army Ranger who taught me a few tricks about running around in the dark, and it's truly amazing how much you can see. A really strong light would blind you to the dim ambient light though, it's all about subtle contrasts. People assume you always need to bring a lot of light to the night, when actually you can often see more with a dim light or none. But then hauling it down a tight trail on a bike is a different thing. Ambient light night riding is a slow and easy paced thing.

Lizzy