I'll admit it's not as easy to advertise some niche directories, but as long as you can find a target audience, it's not that bad. My first attempt at a niche directory is failing miserably, so I ditched it. The difficult part really is finding your niche and advertising it to get people to add their links.
Niche directories are alot harded than general directories, getting submissions is never hard, the problem is that most of them are not relevant. I find myself having to add my own listings just to keep the site updated.
It's not that hard to create a niche directory. However, it is very difficult to maintain one...especially if you use one of the popular directory scripts. The reason for this is that you'll get a ton of spam submissions and very few submissions in your niche. If you can find a topic that you love and build your own software then you'll avoid much of the hassle of running a directory. Then you can focus on marketing your directory instead of spending your time deleting spam submissions.
Creating directory is just 2 second work (just download script and install it) managing directory may be litle hard after directory get popular coz lot of spammer submit thousands of linkdaily