Boy im fond of layers...when i create a job or piece etc i can have 20 or 30 layers without a problem...
if im tracing a bitmap one for each colour ETC...
and often i might have additional effects layers.....interleaved for each colour layer...
Sometimes i have seversal artwork layers some underneath and some ontop so i can quicky flick one off and on to compare ETC...

And sometimes with so many layers quickly effecting many layers is too hard....

I would love if you could assign a category tag to each layer... this could be any identifier a number or word ETC...
Just so you could categorize each layer.....
I.E
1) art
2) art
3) color
4) art
5) effect
6) boarder mask

ETC...
So that by assigning an id tag to each layer you could then quickly select all those layers at one by group...
ie you could have a layer groupings tab that would only display the layer groups ETc or you could just right click on the actual group heading and hide or show all or lock or enable all the selection ETC....

This functionality would greatly assist all the layer lovers out there...... like myself

There's lots of requests to improve layers interface usability, some of them are:

https://bugs.launchpad.net/inkscape/+bug/181578
https://bugs.launchpad.net/inkscape/+bug/171902

but I'm sure there are many more, search for layers in the tracker, maybe there is a request similar to yours.