The name wouldn't have had any value if you had not developed it. It works for what you are doing, though, so congrats on that. It just doesn't have commercial appeal or type-in traffic, so nobody would pay any amount of XX unless they specifically had plans on developing it.
I'm not saying the name doesn't make sense, but I have had thousands of names that have made a lot of sense, and I had to make adjustments over the last few years in my thinking. It is not enough anymore for a name to make a little bit of sense. For a name to be worth anything, you have to imagine being able to get at least low-mid XXX in a lucky end-user sale at some point (if it gets no traffic). This isn't that type of name.
I used to have a name called VarietyMotors.com. There were sites at VarietyMotors.net and VarietyMotors.us, and I held this name for years and wasted a lot of time emailing and thinking about it. At the end I couldn't even get a few hundred out of it, so I just included it in a sale of some 50-60 names I basically gave away. A name like LibraryIndex.com would likely sit around forever. I have had similar names to VarietyMotors.com that I sold for good money, and I kept VarietyMotors.com for a few years because at least the potential for a good sale was there, and it had commercial appeal even to somebody who didn't have the .net or .us. I got tired of looking at it and sent it to a new home.