IMO, L-N.net's are worth a whole lot in terms of traffic. The domain k-9.net could we worth some money, or c-4.net, but unless you have a good acronym, the domain is really only worth what someone wants to pay for having a 3 char domain name. The link listed above gives an idea what 3 chars are going for right now. I have noticed that many people are selling above the listed price on the 3char website.
So to answer your question, they are worth more than reg fee. How much more? It all depends if there is traffic, an acronym, if it is listed in search engines, etc. If it is just the name, you probably could get at least $45 for the domain to the right person.