They are probably setup specifically to build some easy links to then to sell. I doubt they are overly dangerous but I also can't imagine they have a ton of juice. Who knows though, they may be from start ups that had a buzz about them and then never made it to market.
There are lots of genuine reasons that a newish domain could have loads of backlinks and still have been dropped.
My Bro in law, for example, has a fair sized company round here and buys a few domains every year for different specials and events and then lets them drop. In that time there will be some backlinks and content history created, they aren't negative sites but I can't imagine those (specifically) would be worth bothering with.