Tough one, it's one of those common terms that would appear to have value but personally I don't see any use for it.
Google 'admin demo' and you will see how people set up admin demos on their site, either with a subdomain or subdirectory. Doesn't make much sense to send them to admindemo.com which would just take away from the demo experience. There are also no advertisers for this term.
Of course there could always be some new concept that makes it work, especially if you think of one and build it. I say mid-high $xx with potential.