Well, this topic came up on the feeder forum not too long ago so I was able to look this up for you! 
For the low-down on nightcrawlers read this - www.icomm.ca/dragon/wholeprey.htm#earthworms.
And for the nutritional values in comparison with other insects read this - www.icomm.ca/dragon/wholeprey.htm#content.
For that matter, this whole page is very good and is a must read: www.icomm.ca/dragon/wholeprey.htm. Now keep in mind that this article was written for water dragons, a relative and neighbor of the MHD, but it does contain some very good information and is good food for thought since we don't really know what MHDs eat in the wild.
I too feel that these animals should have a varied diet. From what I have found, my dragons all love earthworms. Almost all of my females love pinks but only a couple of my males will even look at them. All of my girls will pounce on the occasional superworm that is uncovered when I change water or replace their food dish. My males will only occasionally eat the supers. My females go nuts over roaches when I add them to the tank but I haven't done so on a regular basis so I am not sure if they would eat them consistently and I haven't yet determined what size they most easily eat.
So, I think we all need to do a lot of work here to determine what is a healthy diet for our MHDs. The original thread on the feeder forum was posted by the owner of a Chinese crocodile lizard and the first respondent stated that "Earthworms are pretty high in calcium & seem to be the predominate food of Shinsaurus." Maybe this is the case with our MHDs as well, but maybe not, and we need to find out. This will only happen with long term captive care and field research, which isn't being done. In the field specimens would be collected and the contents of their stomach analyzed. Now I know this is an unpleasant thought, but it is the only way we would know for certain what MHDs eat in the wild.
Anyway, the nightcrawler may be all that the MHD needs to eat, depends on what is natural for a MHD. It may not be all they need either and that is why most of us do offer other feeders. I have had the best luck with hornworms, superworms, silkworms, pinkies, and roaches. Hornworms are very expensive, about $1 each plus shipping. Superworms are ok but my MHDs eat a few and get tired of them. Silkworms are always well accepted but I have heard from other MHD owners who couldn’t get their animals to look at them and some went so far as to take them and spit them out. The pinkies are usually well taken, if frozen thawed it takes some time to wiggle them to attract the MHDs attention but once they take them they will take them more readily the next time. Roaches always attract my dragons’ attention!
So, If your dragon won’t eat anything but nightcrawlers I wouldn’t worry too much. I would leave the supers in some cricket chow in a dish in the tank and my bet is they will be eaten. If not, don’t buy them again. Give some of these other feeder candidates a try. If you only have one or two dragons, hornworms aren’t such a bad idea. I just can’t afford them when I am feeding 15+ animals. You can get them from Mulberry Farms. Silkworms are a problem for people who only have one or two animals because they can be a huge waste if the animals don’t take to them. I don’t have to worry about that because of my 15+ animals! 
So, I know this is a lot of though and info but every now and again I have to get lost in thought! Hope this helps a little.
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Marcia - FroggieB Dragons
www.froggieb.com/MHDHome.html