Hmm... on the one hand the original DVD is way too dark, but on the other hand, adjusting the levels is going to bring up noise, cause posterisation, etc, so there's a good case to be made for leaving it as is and leaving it to people to adjust their sets. I suspect keeping the original levels will make encoding more efficient, too...
Edit: never mind, I figured out what was wrong with my levels boosting - it looks a lot nicer now so I'm going ahead with it. Spotted something else to correct though...