They're not as valuable as you might think. LL.com's go for >$1M but LL.org's and LL.net's are in the $10K-$50K range.

I missed registering kl.com by a few weeks and had to settle for kl.net. This was back 1995 when you had to email a template to Internic and wait about three weeks for a reply. In the template you had to provide working nameservers. I had put down some random hostnames for nameservers since I wasn't running my own yet and it was rejected after the usual three week delay. By the time I had nameservers set up a few weeks later a law firm had registered kl.com.

With working nameservers I was able to register maj.com (have since sold it) and finally kl.net which I plan to keep til I die.