When is too many lenses a bad thing?

When you don't use all of them and you're running out of cabinet space. I've been cleaning out my camera storage and finding some stuff that I haven't used in some time. Some of them have been quick sells on craigslist (makes me wonder if I'm pricing them too low), and some have been torturous (all these questions from buyers who haven't heard of Google). So far I've managed to sell three lenses in the span of two weeks. That brings my count down to 15 active lenses between two systems (CX: 5 FX: 10).

Now I'm thinking that I still have too many lenses. There are four that I know I haven't used in a year: 

1. Nikon 16mm f/2.8 fisheye

2. Nikon 28-105mm f/3.5~5.6 AF-D

3. Nikon 105mm f/2.8 AF-D micro

4. Sigma 12-24 f/4~5.6 HSM

Why haven't these lenses seen much action? They just don't suit my shooting style, or have a focal length duplicated by other lenses.

But... I'll miss them if I sell them (well, not so much the 28-105mm). There will be that one time that I need a macro lens, or a fisheye, or a really wide rectilinear. That's why I still own them.

Except maybe the 28-105mm will go on craiglist soon.