I suspect the only way to get a good list of projects is to do the leg
work ourselves.
Well I assume we would do an initial list[1]; and then ask the user list if we missed anyone. 
b) if they provide a welcome page we will show the project logo
Instead of the welcome pages, what do you think about just a single
page with a list of projects, each having a few lines of text and
optionally a logo and a small screenshot or other graphic.
That was slightly more work than I wanted to do :-)

I did not want to be responsible for us keeping an up to date description of a project like AtlasStyler.
The only reason I am willing to go out of my way on the welcome pages is because they are focused on
developers and we need volunteers :-)

As for why have a list of projects in the first place? Mostly to show that the library is useful and used.

[1] http://live.osgeo.org/en/overview/geotools_overview.html