In my opinion, they are only worth the cost of a one-year renewal fee, or about $8 each.  The minglemangle.com phrase, unlike the others, however, doesn't describe any thing or any service and, so, is more capable of becoming a protectable trademark than any other the other second-level domains.  If someone has an idea for a site that could use a catchy phrase like "minglemangle" as a domain, he or she may pay a bit more than $8 for it.  I hope that clarifies my last post.  Again, these are just one dotster's opinions.