Funny you should say this, I actually use eggshells in my garden outdoors.....
I think I'm so much more comfortable with outdoor gardening because the plants seem so much more forgiving. Growing indoors, I feel like everything needs to be "measured".
That "everythig needs to be bottled and measured" feeling was definitely how I felt when I first read books on growing and arrived at this website. My first grow, I followed those rules with fairly good results - mostly because I really needed to grow medical marijuana in amounts we can't afford to buy.
Now I have gone the other way, so minimalist (soil, water, and worm castings) that I don't get very good yields. The quality of bud, however, is much superior to the quality of my first 'bottled nutes' buds. I am slowly finding my way to a balance point that works for my garden.
My inputs to the worm trays the last several months has been limitted to:
1. Cannabis leaves and stems
2. Organic bannana peels
3. rock dust (basalt)
4. water
5. crushed egg shells (recently)
I'm sure there is a healthier balance of worm food, but I don't know what that balance should be. Everyone seems to suggest one can put in almost everything except meat and spicy chilis, but no one seems to have a recipe for worm food that will provide optimal worm castings for gardening.